Avoid undefined behavior in vp8 screenshare_layers

webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc

Index: webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc
diff --git a/webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc b/webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc
index f31ed5e4d824b9dc3f5219c6bde10591814556e2..e5e88942e4b88c08eb6433a78ad151bd4a50d021 100644
--- a/webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc
@@ -8,6 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <vector>
+
 #include "gtest/gtest.h"
 #include "vpx/vpx_encoder.h"
 #include "vpx/vp8cx.h"
@@ -41,6 +43,8 @@ class ScreenshareLayerTest : public ::testing::Test {
                    CodecSpecificInfoVP8* vp8_info,
                    int* flags) {
     *flags = layers_->EncodeFlags(timestamp);
+    if (*flags == -1)
+      return;
     layers_->PopulateCodecSpecific(base_sync, vp8_info, timestamp);
     ASSERT_NE(-1, frame_size_);
     layers_->FrameEncoded(frame_size_, timestamp, kDefaultQp);