lavf/vividas: Do not increase extradata_size after allocation.

Avoids a crash in avcodec_parameters_from_context().

libavformat/vividas.c

@@ -392,6 +392,7 @@ static void track_header(VividasDemuxContext *viv, AVFormatContext *s,  uint8_t
                 offset += data_len[j];
             }
 
+            if (offset < st->codecpar->extradata_size)
                 st->codecpar->extradata_size = offset;
         }
     }