set confirm overlay size according to scaled interface

Author: myk002

confirm.lua

@@ -66,7 +66,8 @@ function ConfirmOverlay:init()
 end
 
 function ConfirmOverlay:preUpdateLayout()
-    self.frame.w, self.frame.h = dfhack.screen.getWindowSize()
+    local interface_rect = gui.get_interface_rect()
+    self.frame.w, self.frame.h = interface_rect.width, interface_rect.height
     -- reset frames if any of them have been pushed out of position
     for id, conf in pairs(specs.REGISTRY) do
         if conf.intercept_frame then