Fix #10048: Don't relocate company HQ on the same exact location (#10049)

src/object_cmd.cpp

@@ -328,6 +328,8 @@ CommandCost CmdBuildObject(DoCommandFlag flags, TileIndex tile, ObjectType type,
 		case OBJECT_HQ: {
 			Company *c = Company::Get(_current_company);
 			if (c->location_of_HQ != INVALID_TILE) {
+				/* Don't relocate HQ on the same location. */
+				if (c->location_of_HQ == tile) return_cmd_error(STR_ERROR_ALREADY_BUILT);
 				/* We need to persuade a bit harder to remove the old HQ. */
 				_current_company = OWNER_WATER;
 				cost.AddCost(ClearTile_Object(c->location_of_HQ, flags));