videodec: some extra error checking for sinkpad caps
videodec: some extra error checking for sinkpad caps

In case of an unparsed (raw) mpeg4 stream, we'll get video/mpeg caps from
typefind which do not have width/height set.  In this case we should bail
out with a not-negotiated error, rather than propagating the invalid caps
and crashing in other creative ways.

mrchapp/gst-openmax-devel,mrchapp/gst-openmax-devel,mrchapp/gst-openmax,mrchapp/gst-openmax-devel,mrchapp/gst-openmax,mrchapp/gst-openmax