Fix vpImageConvert::YUYVToRGBa() and YUYVToRGB() color conversion

[fspindle]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 45.20%. Comparing base (2d8f856) to head (ea397a3).
Report is 4 commits behind head on master.

Files	Patch %	Lines
modules/core/src/image/vpImageConvert_yuv.cpp	0.00%	2 Missing ⚠️
...les/sensor/src/framegrabber/v4l2/vpV4l2Grabber.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1432      +/-   ##
==========================================
- Coverage   45.22%   45.20%   -0.03%     
==========================================
  Files        1106     1106              
  Lines      109993   110054      +61     
  Branches    18868    18869       +1     
==========================================
+ Hits        49748    49749       +1     
- Misses      60245    60305      +60     

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