window: Don't accidentally destroy panels when showing overview

When passing --overview, Settings' new shell window accidentally
removes the newly selected panel.

We're considering the possibility of adding an overview page but,
since that won't happen for the next release, let's just make sure
something happens for now.

Fix that by simply changing the panel list view, which selects the
Wi-Fi panel if the user was in another view.

https://bugzilla.gnome.org/show_bug.cgi?id=786117