When you create a dialog, you name it. In your case, you're naming it Query. You can only have one dialog with the same name open at the same time. You would need to create the dialog using a different name. Note your /dialog -m command. You can change the name there and avoid the problem.
One example:
//dialog -m $nick Query
That will name the dialog using $nick and open the Query dialog. As long as you don't want multiple dialogs for that nick open, you're fine. You can name it different ways... just as long as the name is not the same as one that is already open.
Just keep in mind that you are using variables that are static instead of dynamic. If you have more than one dialog open, you will be overwriting those variables. For that matter, you're overwriting them already. You'll need dynamic variables.
