Replace invalid Theora frame rate by 25 FPS.

Avoids division by 0 due to e.g. time_base denominator being 0.

Originally committed as revision 19334 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/oggparsetheora.c

@@ -86,6 +86,11 @@ theora_header (AVFormatContext * s, int idx)
         }
         st->codec->time_base.den = get_bits_long(&gb, 32);
         st->codec->time_base.num = get_bits_long(&gb, 32);
+        if (!(st->codec->time_base.num > 0 && st->codec->time_base.den > 0)) {
+            av_log(s, AV_LOG_WARNING, "Invalid time base in theora stream, assuming 25 FPS\n");
+            st->codec->time_base.num = 1;
+            st->codec->time_base.den = 25;
+        }
         st->time_base = st->codec->time_base;
 
         st->sample_aspect_ratio.num = get_bits_long(&gb, 24);