Fix double MOVED reply on unblock at failover

[zuiderkwast]

#2329 intoduced a bug that causes a blocked client in cluster mode to receive two MOVED redirects instead of one. This was not seen in tests, except in the reply schema validator.

The fix makes sure the client's pending command is cleared after sending the MOVED redirect, to prevent if from being reprocessed.

Fixes #2676.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.60%. Comparing base (ccf6fca) to head (0f55d10).
⚠️ Report is 1 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2734      +/-   ##
============================================
- Coverage     72.60%   72.60%   -0.01%     
============================================
  Files           128      128              
  Lines         71278    71278              
============================================
- Hits          51754    51750       -4     
- Misses        19524    19528       +4     

Files with missing lines	Coverage Δ
src/blocked.c	91.32% <100.00%> (ø)

... and 11 files with indirect coverage changes

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[hpatro]

I believe this needs to be backported by 9.0 GA.