Fix custom order generators for left-click targeting.

OpenRA.Game/Orders/GenericSelectTarget.cs

@@ -58,5 +58,11 @@ namespace OpenRA.Orders
 		{
 			return world.Map.Contains(cell) ? Cursor : "generic-blocked";
 		}
+
+		public override bool InputOverridesSelection(World world, int2 xy, MouseInput mi)
+		{
+			// Custom order generators always override selection
+			return true;
+		}
 	}
 }