feat: 3765 - "red rectangle" possible side-effect fix

[monsieurtanuki]

What

• This is only a quick fix of a possible side-effect (for transparent images) of the crop tool (cf. Requests for reproduction: First picture lost on upload #3904)
• An additional PR will use the latest version of crop_image (which also fixes that bug), but that takes longer to code, so first the quick fix!

Part of

• Use package crop_image instead of local code #3765

[codecov-commenter]

Codecov Report

Merging #3920 (80017af) into develop (e5bf1cb) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #3920   +/-   ##
========================================
  Coverage    10.64%   10.65%           
========================================
  Files          271      271           
  Lines        13478    13474    -4     
========================================
  Hits          1435     1435           
+ Misses       12043    12039    -4     

Impacted Files	Coverage Δ
...pp/lib/tmp_crop_image/rotated_crop_controller.dart	0.00% <ø> (ø)

... and 1 file with indirect coverage changes

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[M123-dev]

👍🏼

[monsieurtanuki]

Thank you @M123-dev for your quick review!