avcodec/speedhq: Width < 8 is not supported

Fixes: out of array access
Fixes: 31733/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SPEEDHQ_fuzzer-4704307963363328
Fixes: 31736/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SPEEDHQ_fuzzer-6190960292790272

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

libavcodec/speedhq.c

@@ -498,7 +498,7 @@ static int speedhq_decode_frame(AVCodecContext *avctx,
     uint32_t second_field_offset;
     int ret;
 
-    if (buf_size < 4)
+    if (buf_size < 4 || avctx->width < 8)
         return AVERROR_INVALIDDATA;
 
     quality = buf[0];