(Wallet) Implement mitigation for null password issue

[simoarpe]

Resolves brave/brave-browser#38224

Resolves brave/brave-browser#38220

Resolves brave/brave-browser#35297

Implement a mitigation for an issue that may cause an illegal state exception during Wallet creation.

When brave/brave-browser#35294 will be completed the Wallet restoration (that most likely was causing the issue) will be refactored.

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• 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 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/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Account Recovery Steps

• Clean Wallet data, if any
• Navigate to Wallet section to trigger onboarding flow
• Tap on restore Wallet and complete onboarding flow
• Observe the Wallet is correctly restored

[github-actions]

The security team is monitoring all repositories for certain keywords. This PR includes the word(s) "password" and so security team members have been added as reviewers to take a look.

No need to request a full security review at this stage, the security team will take a look shortly and either clear the label or request more information/changes.

Notifications have already been sent, but if this is blocking your merge feel free to reach out directly to the security team on Slack so that we can expedite this check.

[SergeyZhukovsky]

++

[simoarpe]

This pull request fixes an issue we wanted to uplift.
What this PR does is preventing access to a field when null causing an exception.

For security reviewer: feel free to verify further, but I think a security review is not needed here.

[kdenhartog]

kicked off a build for this tonight so I can test this in the morning. From a quick look at the code I'm not seeing any issues so far

[kdenhartog]

Tested and not seeing any issues.

[srirambv]

Verification passed on Lenovo Tab with Android 14 running 1.68.34 x64 Nightly build

• Verified steps from PR
• Verified account restore fails when invalid seed phrase is used
• Verified Account recovery failed. Please try again message is shown without navigating to Creating wallet screen
• Verified able to successfully restore wallet with correct seed phrase