Fix bug of get context user

[lunny]

Partially fix #17163

[wxiaoguang]

Should we replace all legacy GetAPIContext with this new one

Should we make GetAPIContext nil-safe?

[codecov-commenter]

Codecov Report

Merging #17169 (22d2a9b) into main (a82c799) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main   #17169      +/-   ##
==========================================
+ Coverage   45.29%   45.31%   +0.01%     
==========================================
  Files         778      778              
  Lines       87194    87195       +1     
==========================================
+ Hits        39496    39511      +15     
+ Misses      41283    41276       -7     
+ Partials     6415     6408       -7     

Impacted Files	Coverage Δ
modules/context/context.go	59.16% <0.00%> (-0.89%)	⬇️
routers/web/base.go	18.00% <0.00%> (+0.85%)	⬆️
modules/git/repo_base_nogogit.go	82.85% <0.00%> (-2.86%)	⬇️
modules/git/utils.go	68.05% <0.00%> (-2.78%)	⬇️
modules/queue/queue_channel.go	95.00% <0.00%> (-1.67%)	⬇️
models/issue_comment.go	51.61% <0.00%> (-0.30%)	⬇️
services/pull/pull.go	42.19% <0.00%> (+0.40%)	⬆️
routers/api/v1/repo/pull.go	29.50% <0.00%> (+0.51%)	⬆️
modules/queue/queue_bytefifo.go	59.88% <0.00%> (+0.59%)	⬆️
models/repo_list.go	78.43% <0.00%> (+0.78%)	⬆️
... and 5 more

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