ext/ogg/gstoggdemux.c: Make sure to remove the pad when a new chain is encountered. Set some vars to NULL so we don't...

Original commit message from CVS:
* ext/ogg/gstoggdemux.c: (gst_ogg_pad_remove),
(gst_ogg_demux_push), (gst_ogg_chains_clear):
Make sure to remove the pad when a new chain is
encountered. Set some vars to NULL so we don't try
to reference freed memory.