videoscale: ignores possible passthrough in fixate_caps
Submitted by Matthew Waters
While implementing bug 756935, I noticed that videoscale ignores the unfixed width/height and ends up scaling itself rather than in the sink.
If upstream has fixed caps (e.g. from a video file) and a preferred width/height in the first structure and unfixed width/height in subsequent structure/s, then videoscale is truncating before attempting to fixate which will lose the unfixed caps.