avcodec/escape124: fix signdness of end of input check

Fixes: Timeout
Fixes: 56561/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ESCAPE124_fuzzer-5560363635834880

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 87ad0a5dd7)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/escape124.c

@@ -89,7 +89,7 @@ static CodeBook unpack_codebook(GetBitContext* gb, unsigned depth,
     unsigned i, j;
     CodeBook cb = { 0 };
 
-    if (size >= INT_MAX / 34 || get_bits_left(gb) < size * 34)
+    if (size >= INT_MAX / 34 || get_bits_left(gb) < (int)size * 34)
         return cb;
 
     if (size >= INT_MAX / sizeof(MacroBlock))