devel/dflayout: fix interface percentage change detection

The interface percentage was not being saved, so it was constantly
initiating updates.

Once the spurious updates were fixed, it uncovered broken update
processing when activating a demo and when the fort toolbar demo was
told to update itself.

Author: ChrisJohnsen

devel/dflayout.lua

@@ -47,6 +47,7 @@ function DemoWindow:init(args)
             on_submit = function(index, item)
                 local demo = self.demos[index]
                 demo.active = demo.available() and not demo.active
+                if demo.active then demo.update() end
                 self:refresh()
             end
         },
@@ -104,6 +105,7 @@ function DemoScreen:render(...)
     if visible_when_not_focused then
         local new_if_percentage = df.global.init.display.max_interface_percentage
         if new_if_percentage ~= if_percentage then
+            if_percentage = new_if_percentage
             self:updateLayout()
         end
     end
@@ -203,6 +205,7 @@ local function update_fort_toolbars(secondary)
         v.subviews.buttons:setText(
             buttons:sub(2) -- the demo panel border is at offset 0, so trim first character to start at offset 1
         )
+        v:updateLayout()
     end
     if secondary then
         -- a secondary toolbar is active, move the primary demonstration up to