smacker: fix integer overflow with pts_inc

Bug-Id: 1073

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Sean McGovern <gseanmcg@gmail.com>

libavformat/smacker.c

@@ -117,6 +117,11 @@ static int smacker_read_header(AVFormatContext *s)
     smk->height = avio_rl32(pb);
     smk->frames = avio_rl32(pb);
     smk->pts_inc = (int32_t)avio_rl32(pb);
+    if (smk->pts_inc > INT_MAX / 100) {
+        av_log(s, AV_LOG_ERROR, "pts_inc %d is too large\n", smk->pts_inc);
+        return AVERROR_INVALIDDATA;
+    }
+
     smk->flags = avio_rl32(pb);
     if(smk->flags & SMACKER_FLAG_RING_FRAME)
         smk->frames++;