avcodec/rasc: Check input size in decode_fint()

Fixes: Timeout (11sec -> 42ms)
Fixes: 18287/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RASC_fuzzer-5637866331308032

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

libavcodec/rasc.c

@@ -124,6 +124,8 @@ static int decode_fint(AVCodecContext *avctx,
         clear_plane(avctx, s->frame1);
         return 0;
     }
+    if (bytestream2_get_bytes_left(gb) < 72)
+        return AVERROR_INVALIDDATA;
 
     bytestream2_skip(gb, 8);
     w = bytestream2_get_le32(gb);