avidemux: avoid invalid H264 bytestream codec_data
avidemux: avoid invalid H264 bytestream codec_data

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=681369

knuesel/gst-plugins-good,knuesel/gst-plugins-good,knuesel/gst-plugins-good,knuesel/gst-plugins-good