Fix crash in fuzz test.

media/filters/ffmpeg_video_decoder.cc

Index: media/filters/ffmpeg_video_decoder.cc
diff --git a/media/filters/ffmpeg_video_decoder.cc b/media/filters/ffmpeg_video_decoder.cc
index 05849f2dd83eb853f489be1b851e4d29a9a3213a..a80c3654459f5345fba5d6f954a71c2f168b8a6d 100644
--- a/media/filters/ffmpeg_video_decoder.cc
+++ b/media/filters/ffmpeg_video_decoder.cc
@@ -133,6 +133,9 @@ int FFmpegVideoDecoder::GetVideoBuffer(struct AVCodecContext* codec_context,
   scoped_refptr<VideoFrame> video_frame = frame_pool_.CreateFrame(
       format, coded_size, gfx::Rect(size), natural_size, kNoTimestamp);
 
+  if (!video_frame)
+    return AVERROR(EINVAL);
+
   // Prefer the color space from the codec context. If it's not specified (or is
   // set to an unsupported value), fall back on the value from the config.
   ColorSpace color_space = AVColorSpaceToColorSpace(codec_context->colorspace,