Fix disable mask for sorter drop-down being mis-aligned.

Sort by length was incorrectly available, and crashed for non ground
vehicles.

src/group_gui.cpp

@@ -586,7 +586,8 @@ public:
 				break;
 
 			case WID_GL_SORT_BY_DROPDOWN: // Select sorting criteria dropdown menu
-				ShowDropDownMenu(this, this->vehicle_sorter_names, this->vehicles.SortType(),  WID_GL_SORT_BY_DROPDOWN, 0, (this->vli.vtype == VEH_TRAIN || this->vli.vtype == VEH_ROAD) ? 0 : (1 << 10));
+				ShowDropDownMenu(this, this->vehicle_sorter_names, this->vehicles.SortType(),  WID_GL_SORT_BY_DROPDOWN, 0,
+						(this->vli.vtype == VEH_TRAIN || this->vli.vtype == VEH_ROAD) ? 0 : this->vehicle_sorter_non_ground_veh_disable_mask);
 				return;
 
 			case WID_GL_ALL_VEHICLES: // All vehicles button

src/vehicle_gui.cpp

@@ -1631,7 +1631,7 @@ public:
 
 			case WID_VL_SORT_BY_PULLDOWN:// Select sorting criteria dropdown menu
 				ShowDropDownMenu(this, this->vehicle_sorter_names, this->vehicles.SortType(), WID_VL_SORT_BY_PULLDOWN, 0,
-						(this->vli.vtype == VEH_TRAIN || this->vli.vtype == VEH_ROAD) ? 0 : (1 << 10));
+						(this->vli.vtype == VEH_TRAIN || this->vli.vtype == VEH_ROAD) ? 0 : this->vehicle_sorter_non_ground_veh_disable_mask);
 				return;
 
 			case WID_VL_LIST: { // Matrix to show vehicles

src/vehicle_gui_base.h

@@ -37,6 +37,7 @@ struct BaseVehicleListWindow : public Window {
 	static const StringID vehicle_depot_name[];
 	static const StringID vehicle_sorter_names[];
 	static GUIVehicleList::SortFunction * const vehicle_sorter_funcs[];
+	const uint vehicle_sorter_non_ground_veh_disable_mask = (1 << 11); // STR_SORT_BY_LENGTH
 
 	BaseVehicleListWindow(WindowDesc *desc, WindowNumber wno) : Window(desc), vli(wno)
 	{