wayland: Don't leak the tmp_keymap

This is a static variable, so setting it every time will leak the
previous one.

gdk/wayland/gdkdisplay-wayland.c

@@ -534,6 +534,7 @@ _gdk_wayland_display_get_keymap (GdkDisplay *display)
   if (core_keyboard)
     return _gdk_wayland_device_get_keymap (core_keyboard);
 
+  if (!tmp_keymap)
     tmp_keymap = _gdk_wayland_keymap_new ();
 
   return tmp_keymap;