extensions: Fix the extensions list when not running gnome-shell
extensions: Fix the extensions list when not running gnome-shell

If you have the browser-plugin installed, but aren't running gnome-shell,
then the plugin will return -1. We shouldn't filter the paginator in this
case.

magcius/sweettooth,GNOME/extensions-web,magcius/sweettooth,GNOME/extensions-web,GNOME/extensions-web,GNOME/extensions-web