Make frames non reference by default, so they are disposed of automatically

in MPV_frame_start() if we break out due to an error at a random place.
Fixes issue334


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@14283 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/h264.c

@@ -2259,6 +2259,7 @@ static int frame_start(H264Context *h){
         memset(h->slice_table, -1, (s->mb_height*s->mb_stride-1) * sizeof(uint8_t));
 
 //    s->decode= (s->flags&CODEC_FLAG_PSNR) || !s->encoding || s->current_picture.reference /*|| h->contains_intra*/ || 1;
+    s->current_picture_ptr->reference= 0;
     return 0;
 }