[Cherry-Pick] Fix proxy panicking when QueryCoord offline (#23257)

[congqixia]

See also #23253 /kind bug

[sre-ci-robot]

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[codecov[bot]]

Codecov Report

Merging #23361 (6631bac) into hotfix-2.2.5 (cf321af) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@               Coverage Diff                @@
##           hotfix-2.2.5   #23361      +/-   ##
================================================
+ Coverage         81.52%   81.53%   +0.01%     
================================================
  Files               709      709              
  Lines            100269   100272       +3     
================================================
+ Hits              81745    81760      +15     
+ Misses            15339    15331       -8     
+ Partials           3185     3181       -4     

Impacted Files	Coverage Δ
internal/proxy/impl.go	80.25% <100.00%> (+0.22%)	:arrow_up:
internal/util/sessionutil/session_util.go	80.51% <100.00%> (ø)

... and 15 files with indirect coverage changes