gst/flv/gstflvdemux.c: Go out of the parse loop as soon as we get an error instead...

gst/flv/gstflvdemux.c: Go out of the parse loop as soon as we get an error instead of parsing until the GstAdapter is...

Original commit message from CVS:
* gst/flv/gstflvdemux.c: (gst_flv_demux_chain):
Go out of the parse loop as soon as we get an error instead
of parsing until the GstAdapter is empty.
Add some explanations about the header and tag size.
Don't print synchronizing message if everything is fine.