avcodec/aliaspixdec: Check input size against minimal picture size

Fixes: Timeout (15sec -> 72ms)
Fixes: 17774/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALIAS_PIX_fuzzer-5193929107963904

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 8c69310477)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/aliaspixdec.c

@@ -62,6 +62,9 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     if (ret < 0)
         return ret;
 
+    if (bytestream2_get_bytes_left(&gb) < width*height / 255)
+        return AVERROR_INVALIDDATA;
+
     ret = ff_get_buffer(avctx, f, 0);
     if (ret < 0)
         return ret;