Memset svc_params in vp9 wrapper to avoid undefined behavior.

webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc

Index: webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
diff --git a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
index 52ea1d63cbe50845424ee9cdef3a16e0003bff36..884196ad7e1a5b0ae4edf77bba831dfb91acec92 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -81,6 +81,7 @@ VP9EncoderImpl::VP9EncoderImpl()
       // Use two spatial when screensharing with flexible mode.
       spatial_layer_(new ScreenshareLayersVP9(2)) {
   memset(&codec_, 0, sizeof(codec_));
+  memset(&svc_internal_.svc_params, 0, sizeof(vpx_svc_extra_cfg_t));
   uint32_t seed = rtc::Time32();
   srand(seed);
 }