lavc: do not override format if neither text nor bitmap codec prop is set

Some decoders may output both, this way the decoder can set it.
Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/utils.c

@@ -2337,7 +2337,10 @@ int avcodec_decode_subtitle2(AVCodecContext *avctx, AVSubtitle *sub,
 
                 av_free_packet(&pkt_recoded);
             }
-            sub->format = !(avctx->codec_descriptor->props & AV_CODEC_PROP_BITMAP_SUB);
+            if (avctx->codec_descriptor->props & AV_CODEC_PROP_BITMAP_SUB)
+                sub->format = 0;
+            else if (avctx->codec_descriptor->props & AV_CODEC_PROP_TEXT_SUB)
+                sub->format = 1;
             avctx->pkt = NULL;
         }