Fix git open close bug

[lunny]

Fix a bug that git pointer may not be close.

[codecov-commenter]

Codecov Report

Merging #12834 into master will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12834      +/-   ##
==========================================
+ Coverage   43.17%   43.21%   +0.04%     
==========================================
  Files         654      654              
  Lines       72218    72218              
==========================================
+ Hits        31177    31208      +31     
+ Misses      35989    35966      -23     
+ Partials     5052     5044       -8     

Impacted Files	Coverage Δ
services/pull/pull.go	42.03% <100.00%> (ø)
models/error.go	35.66% <0.00%> (+0.85%)	⬆️
models/repo_list.go	79.46% <0.00%> (+0.89%)	⬆️
models/notification.go	67.04% <0.00%> (+0.91%)	⬆️
modules/queue/workerpool.go	60.00% <0.00%> (+1.22%)	⬆️
services/pull/check.go	50.00% <0.00%> (+2.30%)	⬆️
modules/notification/ui/ui.go	83.33% <0.00%> (+2.77%)	⬆️
modules/notification/mail/mail.go	37.93% <0.00%> (+3.44%)	⬆️
modules/charset/charset.go	73.03% <0.00%> (+4.49%)	⬆️
modules/indexer/stats/db.go	69.56% <0.00%> (+8.69%)	⬆️
... and 1 more

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