Trap and report error when hostname is null/empty

[bsclifton]

Fixes brave/brave-browser#28940
Fixes brave/brave-browser#29502
Fixes brave/brave-browser#29477

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

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, 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-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

@MadhaviSeelam can reproduce; I think we need her to try

[bsclifton]

Issues discovered by @MadhaviSeelam and shared on employee Slack here:
https://bravesoftware.slack.com/archives/C021S0FN3V1/p1680565130321449

[MadhaviSeelam]

Verified using

Brave | 1.52.18 Chromium: 112.0.5615.49 (Developer Build) (64-bit)
-- | --
Revision | bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS | Windows 11 Version 22H2 (Build 22621.1413)

[kjozwiak]

@MadhaviSeelam also added verification notes via #17919 (comment) using a 1.50.x build that @bsclifton provided.