avcodec/iff: Check input space before loop in decode_delta_d()

Fixes: Timeout (114sec ->108ms)
Fixes: 19290/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5740598116220928

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

libavcodec/iff.c

@@ -1354,6 +1354,9 @@ static void decode_delta_d(uint8_t *dst,
         bytestream2_init(&gb, buf + ofssrc, buf_end - (buf + ofssrc));
 
         entries = bytestream2_get_be32(&gb);
+        if (entries * 8LL > bytestream2_get_bytes_left(&gb))
+            return;
+
         while (entries && bytestream2_get_bytes_left(&gb) >= 8) {
             int32_t opcode  = bytestream2_get_be32(&gb);
             unsigned offset = bytestream2_get_be32(&gb);