fix: use Viewer state to determine current dir

This is more relyable then parsing the window location query for dir:
* ?dir does not change when navigating between files right now
* ?dir is not present when the viewer is used from within other apps.

We used to fallback to the viewer state which solved the latter.
However it is easier and less error prone
to just rely on viewer state in the first place.

Signed-off-by: Azul <azul@riseup.net>

Author: azul