ext/ffmpeg/gstffmpegenc.c: Set chain function before adding pad, fix memleak on error, error out on encode errors bec...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegenc.c: (gst_ffmpegenc_init),
(gst_ffmpegenc_chain_video):
Set chain function before adding pad, fix memleak on error, error
out on encode errors because none of subsequent frames will work
any better (this is not input dependent).