Blender Git Loki

Fix #32763: Image flickering appears if Movie Clip Editor and compositor opened

The issue was caused by compositor was allocating float buffer for image and
then this buffer was filled with data converted from byte buffer.

If display happens at time between float was allocated and it was filled black
areas were appearing on the screen.

Made it so IMB_float_from_rect locks color management thread so display
transform wouldn't use uninitialized buffer anymore.