Proper error message, Check if grab() was successfull

AutonomousMode/Input/input.cpp

     Mat image;
 
     if(!cap.isOpened()) {
-        cout << "Fehler";
+        cout << "Video capture not opened" << std::endl;
         return Mat();
     }
 
-    cap.grab();
+    if(!cap.grab()) {
+        cout << "Could not grab frame from camera" << std::endl;
+        return Mat();
+    }   
     cap.retrieve(image);
-    
     return image;  
 }
 
 void Input::freeWebcam()
 {
     this->cap.release();
-}
+}