avcodec/fic: Check that there is input left in fic_decode_block()

Fixes: Timeout
Fixes: 12450/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FIC_fuzzer-5661984622641152

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 db1c4acd02)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/fic.c

@@ -138,6 +138,9 @@ static int fic_decode_block(FICContext *ctx, GetBitContext *gb,
 {
     int i, num_coeff;
 
+    if (get_bits_left(gb) < 8)
+        return AVERROR_INVALIDDATA;
+
     /* Is it a skip block? */
     if (get_bits1(gb)) {
         /* This is a P-frame. */