Prevent double waitgroup decrement

[zeripath]

A user in discourse has discovered that under heavy loads it is possible to cause a double decrement in the server connection waitgroup.

This PR prevents this.

[codecov-io]

Codecov Report

Merging #10170 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10170      +/-   ##
==========================================
+ Coverage   43.41%   43.43%   +0.01%     
==========================================
  Files         576      576              
  Lines       79642    79642              
==========================================
+ Hits        34580    34590      +10     
+ Misses      40786    40777       -9     
+ Partials     4276     4275       -1

Impacted Files	Coverage Δ
modules/process/manager.go	74.69% <0%> (-3.62%)	⬇️
modules/queue/workerpool.go	45.55% <0%> (-1.07%)	⬇️
models/gpg_key.go	55.37% <0%> (+0.55%)	⬆️
modules/log/event.go	65.64% <0%> (+1.02%)	⬆️
services/pull/check.go	35.8% <0%> (+2.46%)	⬆️
services/pull/patch.go	62.89% <0%> (+2.51%)	⬆️
services/pull/temp_repo.go	31.62% <0%> (+2.56%)	⬆️

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[guillep2k]

The tests that failed before the latest commit (*int32 vs. int32) show that this was a real problem.