Fix valgrind and asan memory leaks and crashes.

libavformat/oggparsetheora.c

 /**
       Copyright (C) 2005  Matthieu CASTET, Alex Beregszaszi
 
       Permission is hereby granted, free of charge, to any person
       obtaining a copy of this software and associated documentation
       files (the "Software"), to deal in the Software without
       restriction, including without limitation the rights to use, copy,
       modify, merge, publish, distribute, sublicense, and/or sell copies
       of the Software, and to permit persons to whom the Software is
       furnished to do so, subject to the following conditions:
@@ skipping 112 matching lines @@
 
     return 1;
 }
 
 static uint64_t
 theora_gptopts(AVFormatContext *ctx, int idx, uint64_t gp, int64_t *dts)
 {
     struct ogg *ogg = ctx->priv_data;
     struct ogg_stream *os = ogg->streams + idx;
     struct theora_params *thp = os->private;
+    if (!thp) return NULL;
     uint64_t iframe = gp >> thp->gpshift;
     uint64_t pframe = gp & thp->gpmask;
 
     if (thp->version < 0x030201)
         iframe++;
 
     if(!pframe)
         os->pflags |= AV_PKT_FLAG_KEY;
 
     if (dts)
         *dts = iframe + pframe;
 
     return iframe + pframe;
 }
 
 const struct ogg_codec ff_theora_codec = {
     .magic = "\200theora",
     .magicsize = 7,
     .header = theora_header,
     .gptopts = theora_gptopts
 };