DV demuxer: Stricter check for avio_read result.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavformat/dv.c

@@ -495,7 +495,7 @@ static int dv_read_header(AVFormatContext *s)
     }
     AV_WB32(c->buf, state);
 
-    if (avio_read(s->pb, c->buf + 4, DV_PROFILE_BYTES - 4) <= 0 ||
+    if (avio_read(s->pb, c->buf + 4, DV_PROFILE_BYTES - 4) != DV_PROFILE_BYTES - 4 ||
         avio_seek(s->pb, -DV_PROFILE_BYTES, SEEK_CUR) < 0)
         return AVERROR(EIO);