Bugfix: Relaunching the client on macOS will show the settings dialog

Relaunching the ownCloud client when it is already running, would
seemingly do nothing at all. To make this more consistent with other
macOS applications, relaunching will now open the settings dialog.

https://github.com/owncloud/client/issues/8377
https://github.com/owncloud/client/pull/8812
