fix: fix GetShardLeaders return empty node list

[weiliu1031]

issue: #32449

to avoid GetShardLeaders return empty node list, this PR add node list check in both client side and server side.

[mergify]

@weiliu1031 E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[mergify]

@weiliu1031 E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[czs007]

/run-cpu-e2e

[codecov]

Codecov Report

Attention: Patch coverage is 41.66667% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 81.40%. Comparing base (c0555d4) to head (0dd2b41).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #32685      +/-   ##
==========================================
- Coverage   81.75%   81.40%   -0.36%     
==========================================
  Files         998      998              
  Lines      124172   124197      +25     
==========================================
- Hits       101519   101102     -417     
- Misses      18792    19212     +420     
- Partials     3861     3883      +22     

Files	Coverage Δ
internal/proxy/lb_policy.go	100.00% <100.00%> (ø)
internal/querycoordv2/services.go	84.92% <0.00%> (-0.78%)	⬇️

... and 43 files with indirect coverage changes

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: czs007, weiliu1031

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]
• internal/querycoordv2/OWNERS [czs007]

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