avcodec/vp8_parser: Do not leave data/size uninitialized

This is identical to what the VP9 parser does

Fixes: 9215/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_LIBVPX_VP8_fuzzer-5768227253649408
Fixes: out of memory access

This may also fix oss fuzz issue 9212

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

libavcodec/vp8_parser.c

@@ -28,6 +28,9 @@ static int parse(AVCodecParserContext *s,
     unsigned int frame_type;
     unsigned int profile;
 
+    *poutbuf      = buf;
+    *poutbuf_size = buf_size;
+
     if (buf_size < 3)
         return buf_size;