fix: skip the empty partition name in the rate limit interceptor

[SimFG]

issue: #30577

[mergify]

@SimFG ut workflow job failed, comment rerun ut can trigger the job again.

[mergify]

@SimFG ut workflow job failed, comment rerun ut can trigger the job again.

[mergify]

@SimFG E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[mergify]

@SimFG E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.79%. Comparing base (ccce1e9) to head (c03ac88).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #32647      +/-   ##
==========================================
- Coverage   81.82%   81.79%   -0.03%     
==========================================
  Files         990      998       +8     
  Lines      124483   124037     -446     
==========================================
- Hits       101852   101460     -392     
+ Misses      18767    18738      -29     
+ Partials     3864     3839      -25     

Files	Coverage Δ
internal/proxy/rate_limit_interceptor.go	100.00% <100.00%> (ø)

... and 217 files with indirect coverage changes

[bigsheeper]

/lgtm

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: czs007, SimFG

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

The pull request process is described here

Needs approval from an approver in each of these files:

• internal/proxy/OWNERS [czs007]

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