Make error output more verbose

source/RobotAPI/components/units/RobotUnit/Devices/ControlDevice.cpp

@@ -90,7 +90,11 @@ namespace armarx
 
     void ControlDevice::addJointController(JointController* jointCtrl)
     {
-        ARMARX_CHECK_IS_NULL(owner);
+        ARMARX_CHECK_IS_NULL_W_HINT(
+            owner,
+            "The ControlDevice '" << getDeviceName()
+            << "' was already added to a RobotUnit! Call addJointController before calling addControlDevice."
+        );
         ARMARX_DEBUG << "adding Controller " << jointCtrl;
         if (!jointCtrl)
         {