Feature/defer net close

[frankegoesdown]

some refactor with defer calls

[Apokalypser]

looks reasonable to me?

[codecov]

Codecov Report

Merging #668 (52693f7) into dev (b182916) will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #668      +/-   ##
==========================================
- Coverage   98.04%   97.97%   -0.08%     
==========================================
  Files          17       19       +2     
  Lines        2049     2220     +171     
==========================================
+ Hits         2009     2175     +166     
- Misses         33       38       +5     
  Partials        7        7              

Impacted Files	Coverage Δ
calib3d.go	84.84% <0.00%> (-15.16%)	⬇️
core.go	100.00% <0.00%> (ø)
imgproc.go	100.00% <0.00%> (ø)
objdetect.go	100.00% <0.00%> (ø)
contrib/bgsegm.go	100.00% <0.00%> (ø)
svd.go	100.00% <0.00%> (ø)
dnn.go	91.01% <0.00%> (+0.94%)	⬆️

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