libnm-glib: get access points in constructor to prevent D-Bus errors

The errors appeared due to calling GetAccessPoints() on removed devices:
nm_device_wifi_get_access_points: error getting access points: Method "GetAccessPoints" with signature "" on interface "org.freedesktop.NetworkManager.Device.Wireless" doesn't exist

libnm-glib/nm-device-wifi.c

@@ -726,6 +726,13 @@ constructor (GType type,
 	                  G_CALLBACK (state_changed_cb),
 	                  NULL);
 
+	/* Get initial access points to prevent possible errors on
+	 * AccessPointRemoved signal processing. We could make D-Bus
+	 * GetAccessPoints() call on a removed WiFi device object (when
+	 * AccessPointRemoved was triggered by removing the device).
+	 */
+	nm_device_wifi_get_access_points (NM_DEVICE_WIFI (object));
+
 	return object;
 }