Android Back button should make reading mode settings window close

[Palloxin]

Describe your suggested feature

1. Open a random chapter
2. Summon reading mode settings and click on the gear icon
3. Click Android back button (android nav bar)
4. The app will exit the chapter instead of closing the reading mode settings

The feature request is about changing this dynamic: in the case i described above, when the reading mode settings are present and the android back button is clicked, make just the settings window close instead of the chapter (reading mode session).

Other details

https://github.com/LNReader/lnreader/assets/75091899/249681bb-3e85-4c6c-887b-08268ffdea39

Acknowledgements

• [X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• [X] I have written a short but informative title.
• [X] If this is an issue with a source, I should be opening an issue in the sources repository.
• [X] I have updated the app to version 1.1.18.
• [X] I will fill out all of the requested information in this form.