avformat/moflex: Check pop_int() for overflow

Fixes: signed integer overflow: 2 * 2132811776 cannot be represented in type 'int'
Fixes: 25722/clusterfuzz-testcase-minimized-ffmpeg_IO_DEMUXER_fuzzer-6221704077246464

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/moflex.c

@@ -62,6 +62,8 @@ static int pop_int(BitReader *br, AVIOContext *pb, int n)
 
         if (ret < 0)
             return ret;
+        if (ret > INT_MAX - value - value)
+            return AVERROR_INVALIDDATA;
         value = 2 * value + ret;
     }