W32: Correctly set maximized window position

Use screen workarea to *also* set the position of a maximized window,
not just its size. Without this the window position defaults to 0:0
(the topleft corner), which is wrong when taskbar is position along the
top or left edge of the screen.

https://bugzilla.gnome.org/show_bug.cgi?id=746821

gdk/win32/gdkevents-win32.c

@@ -3085,6 +3085,8 @@ gdk_event_translate (MSG  *msg,
 	    {
 	      mmi->ptMaxTrackSize.x = moninfo.rcWork.right - moninfo.rcWork.left;
 	      mmi->ptMaxTrackSize.y = moninfo.rcWork.bottom - moninfo.rcWork.top;
+	      mmi->ptMaxPosition.x = moninfo.rcWork.left;
+	      mmi->ptMaxPosition.y = moninfo.rcWork.top;
 	    }
 	  else
 	    {