filmstripdec: 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/filmstripdec.c

@@ -94,7 +94,8 @@ static int read_packet(AVFormatContext *s,
 static int read_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags)
 {
     AVStream *st = s->streams[stream_index];
-    avio_seek(s->pb, FFMAX(timestamp, 0) * st->codec->width * st->codec->height * 4, SEEK_SET);
+    if (avio_seek(s->pb, FFMAX(timestamp, 0) * st->codec->width * st->codec->height * 4, SEEK_SET) < 0)
+        return -1;
     return 0;
 }