Fix bug in random sampling of patch locations in masks for adversarial patch attacks

[beat-buesser]

Description

This pull request fixes a bug in the random sampling of patch locations in masks for adversarial patch attacks.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Project coverage is 85.41%. Comparing base (cf11263) to head (20f8e27).
Report is 9 commits behind head on dev_1.19.0.

Files with missing lines	Patch %	Lines
...ion/adversarial_patch/adversarial_patch_pytorch.py	85.71%	0 Missing and 2 partials ⚠️
...ion/imperceptible_asr/imperceptible_asr_pytorch.py	50.00%	1 Missing ⚠️
...mators/object_detection/pytorch_object_detector.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           dev_1.19.0    #2539   +/-   ##
===========================================
  Coverage       85.41%   85.41%           
===========================================
  Files             334      334           
  Lines           31000    31001    +1     
  Branches         5299     5300    +1     
===========================================
+ Hits            26478    26481    +3     
+ Misses           3054     3053    -1     
+ Partials         1468     1467    -1     

Files with missing lines	Coverage Δ
art/attacks/evasion/saliency_map.py	100.00% <100.00%> (ø)
art/estimators/classification/pytorch.py	86.45% <ø> (ø)
art/estimators/regression/pytorch.py	14.20% <ø> (ø)
...ion/imperceptible_asr/imperceptible_asr_pytorch.py	86.25% <50.00%> (ø)
...mators/object_detection/pytorch_object_detector.py	88.83% <0.00%> (-0.46%)	⬇️
...ion/adversarial_patch/adversarial_patch_pytorch.py	76.35% <85.71%> (ø)

... and 2 files with indirect coverage changes