avformat/cinedec: Fix DoS due to lack of eof check

Fixes: loop.cine

Found-by: Xiaohei and Wangchu from Alibaba Security Team
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/cinedec.c

@@ -267,8 +267,12 @@ static int cine_read_header(AVFormatContext *avctx)
 
     /* parse image offsets */
     avio_seek(pb, offImageOffsets, SEEK_SET);
-    for (i = 0; i < st->duration; i++)
+    for (i = 0; i < st->duration; i++) {
+        if (avio_feof(pb))
+            return AVERROR_INVALIDDATA;
+
         av_add_index_entry(st, avio_rl64(pb), i, 0, 0, AVINDEX_KEYFRAME);
+    }
 
     return 0;
 }