avcodec/txd: Check for input size against the header size.

Fixes: Timeout (21sec -> 80ms)
Fixes: 20673/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_TXD_fuzzer-5177453863763968

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

libavcodec/txd.c

@@ -43,6 +43,9 @@ static int txd_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     int i, j;
     int ret;
 
+    if (avpkt->size < 88)
+        return AVERROR_INVALIDDATA;
+
     ff_texturedsp_init(&dxtc);
 
     bytestream2_init(&gb, avpkt->data, avpkt->size);