fix: app: make SimGenesisAccount.Validate error if .BaseAccount is nil

[odeke-em]

This change ensures that an error is returned, instead of panicking, when SimGenesisAccount.BaseAccount is nil, after invoking .Validate. Found by fuzzing and added the tests in here to catch future regressions.

Fixes #2586

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[odeke-em]

/cc @elias-orijtech

[yaruwangway]

Hi, it seems the test failed, due to fuzz can still assign a nil to types.Int in the coins.

runtime error: invalid memory address or nil pointer dereference

goroutine 50 [running]:
runtime/debug.Stack()
/usr/local/go/src/runtime/debug/stack.go:24 +0x64
github.com/cosmos/gaia/v11/app.TestFuzzGenesisAccountValidate.func1()
/Users/yaruwang/code/gaia/app/app_genesis_fuzz_test.go:25 +0x50
panic({0x1060318c0, 0x106e81580})
/usr/local/go/src/runtime/panic.go:884 +0x204
math/big.(*Int).Sign(...)
/usr/local/go/src/math/big/int.go:41
github.com/cosmos/cosmos-sdk/types.Int.IsZero(...)
/Users/xxx/go/pkg/mod/github.com/cosmos/cosmos-sdk@v0.45.16-ics/types/int.go:188
github.com/cosmos/cosmos-sdk/types.Coin.IsZero(...)
/Users/xxx/go/pkg/mod/github.com/cosmos/cosmos-sdk@v0.45.16-ics/types/coin.go:61
github.com/cosmos/cosmos-sdk/types.Coins.IsZero(...)
/Users/xxx/go/pkg/mod/github.com/cosmos/cosmos-sdk@v0.45.16-ics/types/coin.go:584
github.com/cosmos/gaia/v11/app.SimGenesisAccount.Validate({0x0, {0x14000ca62d0, 0xa, 0xa}, {0x14000ca63c0, 0xa, 0xa}, {0x140001ec540, 0x9, 0x9}, ...})
/Users/xxx/code/gaia/app/genesis_account.go:31 +0x48
github.com/cosmos/gaia/v11/app.TestFuzzGenesisAccountValidate(0x14000c996c0)
/Users/xxx/code/gaia/app/app_genesis_fuzz_test.go:34 +0x170
testing.tRunner(0x14000c996c0, 0x1062200a0)
/usr/local/go/src/testing/testing.go:1576 +0x10c
created by testing.(*T).Run
/usr/local/go/src/testing/testing.go:1629 +0x368
FAIL
exit status 1

[p-offtermatt]

Hi, thanks for your contribution, appreciate it!

I took the liberty of adding the author checklist to your pr, could you fill it out and make sure to check the boxes?

Some additional comments:

• Could you take a look at the lint and test failures? I think the gofuzz package needs to be added to go.sum
• Could you add a changelog entry for the fix?

Thanks again!

[mpoke]

@odeke-em Could you please address the comments above?

[yaruwangway]

Hi, I merge the commits to this PR and fix there. #2690
so close here.