windowManager: Set correct unfullscreen gesture enabled state on startup

The unfullscreen gesture was defaulting to enabled until the first
window focus change. With it now being run in the capture phase, the
gesture was preventing clicks in the top panel except on the activities
button before the first window was opened.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2087>

js/ui/windowManager.js

@@ -954,6 +954,7 @@ var WindowManager = class {
 
         global.display.connect('notify::focus-window', updateUnfullscreenGesture);
         global.display.connect('in-fullscreen-changed', updateUnfullscreenGesture);
+        updateUnfullscreenGesture();
 
         global.stage.add_action_full('unfullscreen', Clutter.EventPhase.CAPTURE, topDragAction);