Circle Hough Transform improvements

[rolalaro]

• Fix segfault that occured when creating a vpCHT using a path towards a JSON file (mp_mask was not set to nullptr)
• Improved the vpCHT tutorial

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 53.88%. Comparing base (e057281) to head (18e43f8).
Report is 29 commits behind head on master.

Files with missing lines	Patch %	Lines
...ules/imgproc/src/vpCircleHoughTransform_common.cpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1499      +/-   ##
==========================================
- Coverage   53.90%   53.88%   -0.02%     
==========================================
  Files         442      442              
  Lines       53793    53793              
==========================================
- Hits        28996    28987       -9     
- Misses      24797    24806       +9     

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