wtvdec: fix memleak on error

Fixes CID718002
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/wtvdec.c

@@ -580,8 +580,10 @@ static AVStream * new_stream(AVFormatContext *s, AVStream *st, int sid, int code
         if (!wst)
             return NULL;
         st = avformat_new_stream(s, NULL);
-        if (!st)
+        if (!st) {
+            av_free(wst);
             return NULL;
+        }
         st->id = sid;
         st->priv_data = wst;
     }