Plane: don't give tuning errors when VTOL inactive

ArduPlane/tuning.cpp

@@ -283,6 +283,11 @@ float AP_Tuning_Plane::controller_error(uint8_t parm)
     // tuning a quadplane and end up with D dominating
     const float max_P_D_ratio = 3.0f;
 
+    if (plane.quadplane.motors->get_throttle() < 0.1f) {
+        // don't report stale errors if not running VTOL motors
+        return 0;
+    }
+        
     switch(parm) {
     // special handling of dual-parameters
     case TUNING_RATE_ROLL_PI: