Ignore Xss idle monitor on wayland

Wayland doesn't provide XScreenSaver Extension.

gajim/common/idle.py

@@ -28,6 +28,8 @@
 from gi.repository import GLib
 from gi.repository import GObject
 
+from gajim.common import app
+from gajim.common.const import Display
 from gajim.common.const import IdleState
 
 log = logging.getLogger('gajim.c.idle')
@@ -317,6 +319,9 @@ def _get_idle_monitor():
         except GLib.Error as error:
             log.info('Idle time via D-Bus (GNOME) not available: %s', error)
 
+        if app.is_display(Display.WAYLAND):
+            return
+
         try:
             return XssIdleMonitor()
         except OSError as error: