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

[SimFG]

issue: https://github.com/milvus-io/milvus/issues/30577

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

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[APPROVALNOTIFIER] This PR is APPROVED

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

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