A footage layer's frame was copied from the footage cache, converted from
its colour profile, then quantised to the project depth in masked_source:
three passes over a 33 MB 1080p float frame. Footage without masks now
comes quantised from one fused pass (Pipe::copy_converted); other source()
callers still get unquantised pixels. Bit-identical (tested at 8/16/32 bpc).
nazar-gavrylyk
b3dc49a0cf