message: [Unit test] Add check to prevent segfault on empty vector.
  We rather have an unmet expectation than let the test crash.
  Cr-Commit-Position: refs/heads/master@{#28651}
diff: @@ -4863,6 +4863,7 @@ TEST_P(PeerConnectionIntegrationTest, GetSourcesVideo) {
  ASSERT_EQ(receiver->media_type(), cricket::MEDIA_TYPE_VIDEO);
  auto sources = receiver->GetSources();
  ASSERT_GT(receiver->GetParameters().encodings.size(), 0u);
  + ASSERT_GT(sources.size(), 0u);
  EXPECT_EQ(receiver->GetParameters().encodings[0].ssrc,
  sources[0].source_id());
  EXPECT_EQ(webrtc::RtpSourceType::SSRC, sources[0].source_type());
  