videodecoder: Don't assume GstVideoChromaSite and GstVideoColorimetry
Even if given GstVideoChromaSite and/or GstVideoColorimetry has unknown
value(s), assumption for an unknown value should be done by subclass or
downstream element, not a role of video decoder. And subclass might
want to output unknown value as is.depends on gst-plugins-ugly!70 (merged)