Fixed crash when a tab is added to saved group

[simonhong]

fix brave/brave-browser#37160

Widget is referred after group button is removed form widget.

Resolves

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:

See the linked issue

[sangwoo108]

LGTM

[LaurenWags]

Verified with

Brave | 1.67.34 Chromium: 124.0.6367.60 (Official Build) nightly (x86_64)
-- | --
Revision | 54f7c66f9f8a11b6f4fd36c6b3abc37841e4d19f
OS | macOS Version 13.6.6 (Build 22G630)

Used STR from brave/brave-browser#37160 (comment) but was not able to reproduce the crash on the following versions: 1.65.90, 1.65.114, 1.67.18.

Verified when using STR from brave/brave-browser#37160 (comment) and 1.67.34, there is no crash.

[MadhaviSeelam]

Reproduced the issue in Win 11 x64 using both 1.67.18 & 1.65.118.
Verified the issue in 1.67.35 and no crash occurred.