avcodec/cinepak: Check available input against encoded buffer size

Fixes: Timeout (12sec -> 2sec)
Fixes: 14606/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_CINEPAK_fuzzer-5738687561728000

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

libavcodec/cinepak.c

@@ -323,6 +323,9 @@ static int cinepak_predecode_check (CinepakContext *s)
     num_strips  = AV_RB16 (&s->data[8]);
     encoded_buf_size = AV_RB24(&s->data[1]);
 
+    if (s->size < encoded_buf_size * (int64_t)(100 - s->avctx->discard_damaged_percentage) / 100)
+        return AVERROR_INVALIDDATA;
+
     /* if this is the first frame, check for deviant Sega FILM data */
     if (s->sega_film_skip_bytes == -1) {
         if (!encoded_buf_size) {