fix: [2.4] restore rbac with empty meta panic

[shaoting-huang]

cp from master: #39141
related: #38985

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: shaoting-huang
To complete the pull request process, please assign xiaofan-luan after the PR has been reviewed.
You can assign the PR to them by writing /assign @xiaofan-luan in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[mergify]

@shaoting-huang Please associate the related pr of master to the body of your Pull Request. (eg. “pr: #”)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.43%. Comparing base (782cd74) to head (41fc1af).

Additional details and impacted files

@@            Coverage Diff             @@
##              2.4   #39142      +/-   ##
==========================================
- Coverage   80.43%   80.43%   -0.01%     
==========================================
  Files        1077     1077              
  Lines      169720   169723       +3     
==========================================
- Hits       136518   136513       -5     
- Misses      28713    28716       +3     
- Partials     4489     4494       +5     

Files with missing lines	Coverage Δ
internal/metastore/kv/rootcoord/kv_catalog.go	82.20% <100.00%> (ø)
internal/proxy/impl.go	83.87% <100.00%> (+<0.01%)	⬆️

... and 36 files with indirect coverage changes