`Back` should go to parent folder, not exit app

[bilogic]

Describe the bug

If I'm in a nested folder, back should go to the parent of the folder, not exit the app

Steps to reproduce

1. Create a 3 layer deep subfolder structure, A -> B -> C
2. Go to C
3. Tap Android's back, and we exit the app

Expected behavior

We should go to B then A, not exit

Actual behavior

We exit the app instead of going to B

Setup

Just install and create subfolders

Additional context

No

[guruz]

Related PR; #226