flvdemux: Don't create AAC/H264 caps without codec_data
flvdemux: Don't create AAC/H264 caps without codec_data

Instead delay creating the caps until we read the codec_data from the stream,
or fail if we get normal data before the codec_data.

AAC raw caps and H264 avc caps always need codec_data, setting caps on the pad
without them is going to make negotiation fail most of the time. Even if we
later set new caps with the codec_data, that's usually going to be too late.

https://bugzilla.gnome.org/show_bug.cgi?id=746682

StreamUtils/gst-plugins-good,GStreamer/gst-plugins-good,froggatt/gst-plugins-good-m,StreamUtils/gst-plugins-good,sh0/gst-plugins-good,BigBrother-International/gst-plugins-good,kittee/gst-plugins-good,chamois94/gst-plugins-good,sebras/gst-plugins-good,Kurento/gst-plugins-good,stfl/gst-plugins-good,froggatt/gst-plugins-good-m,loshca/gst-plugins-good,pexip/gst-plugins-good,sh0/gst-plugins-good,sebras/gst-plugins-good,kittee/gst-plugins-good,sh0/gst-plugins-good,chamois94/gst-plugins-good,hizukiayaka/gst-plugins-good,froggatt/gst-plugins-good-m,hizukiayaka/gst-plugins-good,rawoul/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,vatavuserban/gst-plugins-good,rawoul/gst-plugins-good,StreamUtils/gst-plugins-good,Kurento/gst-plugins-good,GrokImageCompression/gst-plugins-good,shelsonjava/gst-plugins-good,pexip/gst-plugins-good,StreamUtils/gst-plugins-good,GrokImageCompression/gst-plugins-good,chamois94/gst-plugins-good,stfl/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,GStreamer/gst-plugins-good,Kurento/gst-plugins-good,ikonst/gst-plugins-good,kittee/gst-plugins-good,pexip/gst-plugins-good,vatavuserban/gst-plugins-good,Kurento/gst-plugins-good,stfl/gst-plugins-good,shelsonjava/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,loshca/gst-plugins-good,GrokImageCompression/gst-plugins-good,GStreamer/gst-plugins-good,sebras/gst-plugins-good,ikonst/gst-plugins-good,shelsonjava/gst-plugins-good,stfl/gst-plugins-good,pexip/gst-plugins-good,vatavuserban/gst-plugins-good,GrokImageCompression/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,chamois94/gst-plugins-good,rawoul/gst-plugins-good,sebras/gst-plugins-good,vatavuserban/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,ikonst/gst-plugins-good,Kurento/gst-plugins-good,hizukiayaka/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,BigBrother-International/gst-plugins-good,loshca/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,BigBrother-International/gst-plugins-good,loshca/gst-plugins-good,pexip/gst-plugins-good,froggatt/gst-plugins-good-m,GStreamer/gst-plugins-good,hizukiayaka/gst-plugins-good,sh0/gst-plugins-good,shelsonjava/gst-plugins-good,rawoul/gst-plugins-good,ikonst/gst-plugins-good,kittee/gst-plugins-good,BigBrother-International/gst-plugins-good