Blender Git Loki

Fix T78867: Crash related to viewing video files

Any time FFmpeg was used to get a picture Blender would crash
when FFmpeg 4.3 is used. This affects thumbnails, VSE, Clip Editor.

Caused by a bug in FFmpeg which lead to crashes when unaligned
buffer was passed to sws_scale(). It got fixed later on in FFmpeg,
but for portability and compatibility reasons still nice to avoid
crash, especially since it's not so difficult to do.

FFmpeg ticked number is #8747
The FFmpeg Git hash with the fix: ba3e771a42c2

Differential Revision: https://developer.blender.org/D8355