Allow FetchBalance to return an empty ledger::BalancePtr

[zenparsing]

Resolves brave/brave-browser#10983

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. For instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-compatibility-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

• Start browser with a clean profile.
• Enable rewards.
• Quit browser.
• Open Preferences file and edit the following values:
  • Set "payment_id" to an empty string "".
  • Set "fetch_old_balance" to true.
• Start browser and open rewards panel.
  • Verify that browser does not crash.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated.

[emerick]

LGTM

[zenparsing]

CI failed on unrelated Linux:NotVerifiedWallet

[kjozwiak]

Reproduced the issue on macOS 10.10.6 x64 using the following build:

Brave	1.14.2 Chromium: 84.0.4147.105 (Official Build) nightly (64-bit)
Revision	a6b12dfad6663f13a7e16e9a42a6a4975374096b-refs/branch-heads/4147@{#943}
OS	macOS Version 10.15.6 (Build 19G73)

Used the STR outlined via #6251 (comment) and crashed rewards as per:

https://brave.sp.backtrace.io/p/brave/debug?filters=(_rxid%3D%226f290000-45d5-d704-0000-000000000000%22)&fingerprint=0000000000000000000000000000000000000000000000000000000000000141&debug=(%2250e00%22,0,0)

[ 00 ] crash_reporter::DumpWithoutCrashing()
[ 01 ] base::debug::DumpWithoutCrashing()
[ 02 ] content::BrowserChildProcessHostImpl::OnMojoError(base::WeakPtr<content::BrowserChildProcessHostImpl>, scoped_refptr<base::SingleThreadTaskRunner>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)
[ 03 ] base::internal::Invoker<base::internal::BindState<void (*)(base::WeakPtr<content::BrowserChildProcessHostImpl>, scoped_refptr<base::SingleThreadTaskRunner>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&), base::WeakPtr<content::BrowserChildProcessHostImpl>, scoped_refptr<base::SingleThreadTaskRunner> >, void (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)>::Run(base::internal::BindStateBase*, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)
[ 04 ] mojo::(anonymous namespace)::RunErrorCallback(unsigned long, MojoProcessErrorDetails const*)
[ 05 ] mojo::core::(anonymous namespace)::RunMojoProcessErrorHandler(mojo::core::(anonymous namespace)::ProcessDisconnectHandler*, void (*)(unsigned long, MojoProcessErrorDetails const*), unsigned long, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)
[ 06 ] mojo::core::NodeChannel::NotifyBadMessage(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)
[ 07 ] mojo::core::NodeController::NotifyBadMessageFrom(mojo::core::ports::NodeName const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)
[ 08 ] mojo::core::Core::NotifyBadMessage(unsigned long, char const*, unsigned long, MojoNotifyBadMessageOptions const*)
[ 09 ] mojo::internal::ReportValidationError(mojo::internal::ValidationContext*, mojo::internal::ValidationError, char const*)
[ 10 ] <name omitted>
[ 11 ] bat_ledger::mojom::internal::BatLedger_FetchBalance_ResponseParams_Data::Validate(void const*, mojo::internal::ValidationContext*)
[ 12 ] mojo::internal::ValidateResponseGeneric(mojo::Message*, char const*, base::span<std::__1::pair<unsigned int, mojo::internal::GenericValidationInfo> const, 18446744073709551615ul>)
[ 13 ] mojo::MessageDispatcher::Accept(mojo::Message*)
[ 14 ] mojo::internal::MultiplexRouter::ProcessIncomingMessage(mojo::internal::MultiplexRouter::MessageWrapper*, mojo::internal::MultiplexRouter::ClientCallBehavior, base::SequencedTaskRunner*)
[ 15 ] mojo::internal::MultiplexRouter::Accept(mojo::Message*)
[ 16 ] mojo::Connector::DispatchMessage(mojo::Message)
[ 17 ] mojo::Connector::ReadAllAvailableMessages()
[ 18 ] base::TaskAnnotator::RunTask(char const*, base::PendingTask*)
[ 19 ] base::sequence_manager::internal::ThreadControllerWithMessagePumpImpl::DoWorkImpl(base::sequence_manager::LazyNow*)
[ 20 ] base::sequence_manager::internal::ThreadControllerWithMessagePumpImpl::DoWork()
[ 21 ] invocation function for block in base::MessagePumpCFRunLoopBase::RunWorkSource(void*)
[ 22 ] base::mac::CallWithEHFrame(void () block_pointer)
[ 23 ] base::MessagePumpCFRunLoopBase::RunWorkSource(void*)
[ 24 ] 0x7fff36334d52
[ 25 ] 0x7fff36334cf1
[ 26 ] 0x7fff36334b0b
[ 27 ] 0x7fff3633383a
[ 28 ] 0x7fff36332e3e
[ 29 ] RunCurrentEventLoopInMode
[ 30 ] ReceiveNextEventCommon
[ 31 ] _BlockUntilNextEventMatchingListInModeWithFilter
[ 32 ] _DPSNextEvent
[ 33 ] -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:]
[ 34 ] __71-[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:]_block_invoke
[ 35 ] base::mac::CallWithEHFrame(void () block_pointer)
[ 36 ] -[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:]
[ 37 ] -[NSApplication run]
[ 38 ] base::MessagePumpNSApplication::DoRun(base::MessagePump::Delegate*)
[ 39 ] base::MessagePumpCFRunLoopBase::Run(base::MessagePump::Delegate*)
[ 40 ] base::sequence_manager::internal::ThreadControllerWithMessagePumpImpl::Run(bool, base::TimeDelta)
[ 41 ] base::RunLoop::Run()
[ 42 ] ChromeBrowserMainParts::MainMessageLoopRun(int*)
[ 43 ] content::BrowserMainLoop::RunMainMessageLoopParts()
[ 44 ] content::BrowserMainRunnerImpl::Run()
[ 45 ] content::BrowserMain(content::MainFunctionParams const&)
[ 46 ] content::ContentMainRunnerImpl::RunServiceManager(content::MainFunctionParams&, bool)
[ 47 ] content::ContentMainRunnerImpl::Run(bool)
[ 48 ] service_manager::Main(service_manager::MainParams const&)
[ 49 ] content::ContentMain(content::ContentMainParams const&)
[ 50 ] ChromeMain
[ 51 ] main
[ 52 ] start

Verification PASSED on macOS 10.15.5 x64 using the following build:

Brave | 1.14.18 Chromium: 84.0.4147.105 (Official Build) nightly (64-bit)
-- | --
Revision | a6b12dfad6663f13a7e16e9a42a6a4975374096b-refs/branch-heads/4147@{#943}
OS | macOS Version 10.15.6 (Build 19G73)

Ensured that the above crash wasn't occurring when following the STR/Cases outlined via #6251 (comment).