mpeg2dec: fix spurious failure to decode some files
mpeg2dec: fix spurious failure to decode some files

Parsing can return with an 'invalid' state, but this is not
actually fatal. For one, the mpeg2dec command line tool that
comes with the libmpeg2 library blithely ignores this condition
and merrily goes on. So we do this same, logging the error,
and going on with parsing. This makes something work that did
not use to work, and brings happiness to the world.

https://bugzilla.gnome.org/show_bug.cgi?id=429476

shelsonjava/gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer-sdk__gst-plugins-ugly,sebras/gst-plugins-ugly,alessandrod/gst-plugins-ugly,collects/gst-plugins-ugly,sebras/gst-plugins-ugly,matsu/gst-plugins-ugly,jar1karp/gst-plugins-ugly,Distrotech/gst-plugins-ugly,jpakkane/gstreamer-plugins-ugly,freedesktop-unofficial-mirror/gstreamer-sdk__gst-plugins-ugly,knuesel/gst-plugins-ugly,krieger-od/gst-plugins-ugly,GrokImageCompression/gst-plugins-ugly,shelsonjava/gst-plugins-ugly,Lachann/gst-plugins-ugly,StreamUtils/gst-plugins-ugly,GrokImageCompression/gst-plugins-ugly,collects/gst-plugins-ugly,surround-io/gst-plugins-ugly,GStreamer/gst-plugins-ugly,Distrotech/gst-plugins-ugly,jar1karp/gst-plugins-ugly,ylatuya/gst-plugins-ugly,Kurento/gst-plugins-ugly,shelsonjava/gst-plugins-ugly,GStreamer/gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer__gst-plugins-ugly,krieger-od/gst-plugins-ugly,sebras/gst-plugins-ugly,cablelabs/gst-plugins-ugly,fluendo/gst-plugins-ugly,StreamUtils/gst-plugins-ugly,fluendo/gst-plugins-ugly,alessandrod/gst-plugins-ugly,Lachann/gst-plugins-ugly,matsu/gst-plugins-ugly,fluendo/gst-plugins-ugly,surround-io/gst-plugins-ugly,GStreamer/gst-plugins-ugly,alessandrod/gst-plugins-ugly,krieger-od/gst-plugins-ugly,Lachann/gst-plugins-ugly,krieger-od/gst-plugins-ugly,jpakkane/gstreamer-plugins-ugly,reynaldo-samsung/gst-plugins-ugly,Distrotech/gst-plugins-ugly,GrokImageCompression/gst-plugins-ugly,cablelabs/gst-plugins-ugly,knuesel/gst-plugins-ugly,ylatuya/gst-plugins-ugly,jpakkane/gstreamer-plugins-ugly,reynaldo-samsung/gst-plugins-ugly,Distrotech/gst-plugins-ugly,jar1karp/gst-plugins-ugly,matsu/gst-plugins-ugly,collects/gst-plugins-ugly,knuesel/gst-plugins-ugly,cablelabs/gst-plugins-ugly,surround-io/gst-plugins-ugly,collects/gst-plugins-ugly,Kurento/gst-plugins-ugly,reynaldo-samsung/gst-plugins-ugly,ylatuya/gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer__gst-plugins-ugly,Kurento/gst-plugins-ugly,matsu/gst-plugins-ugly,Distrotech/gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer__gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer-sdk__gst-plugins-ugly,StreamUtils/gst-plugins-ugly