API: GetReleaseByID return 404 if not found

[6543]

as title

[codecov-commenter]

Codecov Report

Merging #12933 into master will decrease coverage by 0.00%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master   #12933      +/-   ##
==========================================
- Coverage   43.09%   43.08%   -0.01%     
==========================================
  Files         658      658              
  Lines       72455    72456       +1     
==========================================
- Hits        31226    31221       -5     
- Misses      36175    36179       +4     
- Partials     5054     5056       +2     

Impacted Files	Coverage Δ
routers/api/v1/repo/release.go	33.60% <33.33%> (+0.54%)	⬆️
modules/charset/charset.go	68.53% <0.00%> (-4.50%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️

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