jvdec: Check return value of avio_seek and avoid modifying state if it fails

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Justin Ruggles <justin.ruggles@gmail.com>

libavformat/jvdec.c

@@ -207,10 +207,11 @@ static int read_seek(AVFormatContext *s, int stream_index,
 
     if (i < 0 || i >= ast->nb_index_entries)
         return 0;
+    if (avio_seek(s->pb, ast->index_entries[i].pos, SEEK_SET) < 0)
+        return -1;
 
     jv->state = JV_AUDIO;
     jv->pts   = i;
-    avio_seek(s->pb, ast->index_entries[i].pos, SEEK_SET);
     return 0;
 }