Not calling waitKey if no output is shown.

.travis.yml

@@ -7,7 +7,7 @@ branches:
   only:
     - master
     - develop
-    - feature/travis_fixes
+    - feature/no-ui-fix
 compiler:
   - gcc
 

lib/local/Utilities/src/Visualizer.cpp

@@ -418,23 +418,37 @@ void Visualizer::SetFps(double fps)
 
 char Visualizer::ShowObservation()
 {
+	bool ovservation_shown = false;
+
 	if (vis_align && !aligned_face_image.empty())
 	{
 		cv::imshow("sim_warp", aligned_face_image);
+		ovservation_shown = true;
 	}
 	if (vis_hog && !hog_image.empty())
 	{
 		cv::imshow("hog", hog_image);
+		ovservation_shown = true;
 	}
 	if (vis_aus && !action_units_image.empty())
 	{
 		cv::imshow("action units", action_units_image);
+		ovservation_shown = true;
 	}
 	if (vis_track)
 	{
 		cv::imshow("tracking result", captured_image);
+		ovservation_shown = true;
 	}
-	return cv::waitKey(1);
+	
+	// Only perform waitKey if something was shown
+	char result = '\0';
+	if (ovservation_shown)
+	{
+		result = cv::waitKey(1);
+	}
+	return result;
+
 }
 
 cv::Mat Visualizer::GetVisImage()