Save desktop width setting

The 2 seconds is arbitrarily chosen. The problem seems to be that
Valve's own overlays are not being initialized before custom overlays,
leading to the Desktop overlay sometimes not being present when our
overlay initializes.

The second if statement inside the first one checking a second time is
definitely a little disgusting, but for now it gets the job done.

The 4.0 default was arbitrarily chosen by whoever decided to initialize
the variable in the class.

src/tabcontrollers/UtilitiesTabController.h

@@ -33,7 +33,7 @@ class UtilitiesTabController : public QObject
             setSteamDesktopOverlayWidth NOTIFY steamDesktopOverlayWidthChanged )
 
 private:
-    void setUpDesktopOverlay();
+    void setUpDesktopOverlay( float desktopWidthInMeters );
 
     OverlayController* m_parent;
     QQuickWindow* m_widget;