Fix crash and show error message if group creation fails

src/group_cmd.cpp

@@ -770,11 +770,12 @@ void GetAutoGroupMostRelevantTowns(const Vehicle *vehicle, Town* &from, Town* &t
 	for (int x = 0; x < num; x++)
 	{
 		Order *order = vehicle->GetOrder(x);
+
+		if (order->GetType() != OT_GOTO_STATION) continue;
+
 		const DestinationID dest = order->GetDestination();
 		Town *town = GetTownFromDestination(dest);
 
-		if (order->GetType() == OT_GOTO_DEPOT) continue;
-
 		if (town != nullptr && unique_destinations.end() == std::find(unique_destinations.begin(), unique_destinations.end(), town))
 		{
 			unique_destinations.push_back(town);
@@ -807,18 +808,19 @@ CommandCost CmdCreateGroupAutoName(TileIndex tile, DoCommandFlag flags, uint32 p
 
 	if (vehicle == nullptr) return CMD_ERROR;
 	if (vehicle->owner != _current_company || !vehicle->IsPrimaryVehicle()) return CMD_ERROR;
+	if (!Group::CanAllocateItem()) return CMD_ERROR;
 
-	if (flags & DC_EXEC) {
-		Town *town_from = nullptr;
-		Town *town_to = nullptr;
-		
-		GetAutoGroupMostRelevantTowns(vehicle, town_from, town_to);
+	Town *town_from = nullptr;
+	Town *town_to = nullptr;
+	
+	GetAutoGroupMostRelevantTowns(vehicle, town_from, town_to);
 
-		if (town_from == nullptr) return CMD_ERROR;
+	if (town_from == nullptr) return CMD_ERROR;
 
+	if (flags & DC_EXEC) {
 		const auto new_group = CreateVehicleAutoGroup(vehicle, town_from, town_to);
 
-		if (new_group == nullptr) return CMD_ERROR;
+		assert(new_group != nullptr);
 
 		AddVehicleToGroup(vehicle, new_group->index);
 

src/group_gui.cpp

@@ -999,13 +999,13 @@ public:
 				}
 				break;
 			}
-			case WID_GL_CREATE_GROUP: { // make new group with vehicle specific name and add vehicle
+			case WID_GL_CREATE_GROUP: { // make new group with auto generated vehicle specific name and add vehicle
 				const VehicleID vindex = this->vehicle_sel;
 				this->vehicle_sel = INVALID_VEHICLE;
 				this->group_over = INVALID_GROUP;
 				this->SetDirty();
 
-				DoCommandP(0, vindex | (_ctrl_pressed ? 1 << 31 : 0),0 , CMD_CREATE_GROUP_AUTO_NAME, nullptr, nullptr);
+				DoCommandP(0, vindex | (_ctrl_pressed ? 1U << 31 : 0),0 , CMD_CREATE_GROUP_AUTO_NAME | CMD_MSG(STR_ERROR_GROUP_CAN_T_CREATE), nullptr, nullptr);
 				
 				break;
 			}