Fixed segfault on corrupted sega streams in the demuxer.

Signed-off-by: Janne Grunau <janne-libav@jannau.net>

libavformat/segafilm.c

@@ -176,6 +176,8 @@ static int film_read_header(AVFormatContext *s,
     if(film->sample_count >= UINT_MAX / sizeof(film_sample))
         return -1;
     film->sample_table = av_malloc(film->sample_count * sizeof(film_sample));
+    if (!film->sample_table)
+        return AVERROR(ENOMEM);
 
     for(i=0; i<s->nb_streams; i++)
         av_set_pts_info(s->streams[i], 33, 1, film->base_clock);
@@ -199,7 +201,7 @@ static int film_read_header(AVFormatContext *s,
             if (film->audio_type == CODEC_ID_ADPCM_ADX)
                 audio_frame_counter += (film->sample_table[i].sample_size * 32 /
                     (18 * film->audio_channels));
-            else
+            else if (film->audio_type != CODEC_ID_NONE)
                 audio_frame_counter += (film->sample_table[i].sample_size /
                     (film->audio_channels * film->audio_bits / 8));
         } else {