Don't emit useless signal

src/Vehicle/MultiVehicleManager.cc

@@ -149,6 +149,7 @@ void MultiVehicleManager::_deleteVehiclePhase2  (void)
 void MultiVehicleManager::setActiveVehicle(Vehicle* vehicle)
 {
     if (vehicle != _activeVehicle) {
+        if (_activeVehicle) {
             // The sequence of signals is very important in order to not leave Qml elements connected
             // to a non-existent vehicle.
             
@@ -158,6 +159,7 @@ void MultiVehicleManager::setActiveVehicle(Vehicle* vehicle)
             _parameterReadyVehicleAvailable = false;
             emit activeVehicleAvailableChanged(false);
             emit parameterReadyVehicleAvailableChanged(false);
+        }
         
         // See explanation in _deleteVehiclePhase1
         _vehicleBeingSetActive = vehicle;