Fix: #11329: Don't assert vehicle list length is non-zero when only asked to set string parameter. (#11330)

Since #11321, the vehicle list is not yet initialized when SetStringParameters is called, so a test that the vehicle list size is zero is triggered. However, doing this check in the SetStringParameters function is a bit out of its remit, so just remove it.

src/vehicle_gui.cpp

@@ -1936,11 +1936,6 @@ public:
 			case WID_VL_CAPTION_SHARED_ORDERS: {
 				switch (this->vli.type) {
 					case VL_SHARED_ORDERS: // Shared Orders
-						if (this->vehicles.size() == 0) {
-							/* We can't open this window without vehicles using this order
-							 * and we should close the window when deleting the order. */
-							NOT_REACHED();
-						}
 						SetDParam(0, this->vehicles.size());
 						break;