core/ImageProcessor.cpp:
- between lines 170-200
- variable forcedAlphaMasking is identical in function to config
  variable binaryMasking. No need to have 2 such variables

gui/MainWindow.cpp:
- lines 603/636

Behavior is now correct in live mode and in batch mode. However,
it is still incomplete. After overriding the alpha value (mask),
the updated mask does not get saved in the project file. Maybe
this is intended this way, or maybe not. I would opt to save the
updated mask, but since the mask override is always done upon
reading the project file, it doesn't really matter.