Fix Mask/Transitions for Global Timeline Effects

[jonoomph]

Refactor of global timeline effects, to address a regression with global/timeline Mask/Transitions no longer working correctly. This was caused by an optimization that broke the general behavior of the global transitions.

[codecov]

Codecov Report

Merging #675 (a505f87) into develop (6a004ed) will increase coverage by 0.01%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop     #675      +/-   ##
===========================================
+ Coverage    52.38%   52.39%   +0.01%     
===========================================
  Files          151      151              
  Lines        12345    12367      +22     
===========================================
+ Hits          6467     6480      +13     
- Misses        5878     5887       +9     

Impacted Files	Coverage Δ
src/Clip.h	75.00% <ø> (ø)
src/Timeline.h	63.63% <ø> (ø)
src/Clip.cpp	42.06% <46.15%> (-0.17%)	⬇️
src/Timeline.cpp	41.70% <90.90%> (+0.09%)	⬆️
src/Settings.h	50.00% <0.00%> (ø)
src/Settings.cpp	100.00% <0.00%> (ø)
tests/Settings.cpp	100.00% <0.00%> (ø)

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[ferdnyc]

@jonoomph It might be a good idea to make the new GetFrame signature a protected method (and friend class the callers that need access). Right now it's ending up in the Python API, and I don't even want to think about how that works when passing a pointer to a struct as one of the arguments.

[ferdnyc]

Huh! Well, apparently it works fine. SWIG, you so crazy.

>>> import openshot
>>> c = openshot.Clip("/var/tmp/pix_scale.mp4")
>>> c.Open()
>>> st = openshot.TimelineInfoStruct()
>>> st.timeline_frame_number = 27
>>> st.is_top_clip = True
>>> f = c.GetFrame(openshot.Frame(), 1, st)

The returned f is a perfectly valid 1px × 1px (due to the default-constructed background_frame) instance of openshot.Frame.

So, I guess it's dealer's choice whether the new GetFrame should be part of the public API, or if it's really meant for TimelineBase internal use only.

[jonoomph]

Thanks for the feedback @ferdnyc! Merged!