Inform user when configuration could not be written (Linux)

[storca]

Expected behaviour

Tell the user when the configuration could not be written (on the client).

Actual behaviour

The client does not save the configuration, consequently, the client asks every time to enter details about server, user, password etc...
It does not save the configuration on exit and goes over the same process over and over again.

Steps to reproduce

1. Make sure the directory ~/.local/share/data/Nextcloud does not exists (if you delete it, it will delete your configuration)
2. Run nextcloud appimage as root
3. The directory ~/.local/share/data/Nextcloud is created with it's config file
4. Close nextcloud client
5. Open the client with your current user (not root)
6. Follow configuration process
   Then, files are syncing as expected
7. Restart nextloud
8. Configuration was not saved

Client configuration

Client version: 2.3.3 build 1

Operating system: Ubuntu 18.04

OS language:

Qt version used by client package (Linux only, see also Settings dialog): 5.9.2

Client package (From Nextcloud or distro) (Linux only): Appimage

Installation path of client:

Server configuration

Operating system:

Web server:

Database:

PHP version:

Nextcloud version: 14.0.3

Storage backend (external storage):

Logs

Please use Gist (https://gist.github.com/) or a similar code paster for longer
logs.

Template for output < 10 lines

1. Client logfile: Output of nextcloud --logwindow or nextcloud --logfile log.txt
   (On Windows using cmd.exe, you might need to first cd into the Nextcloud directory)
   (See also https://docs.nextcloud.com/desktop/2.3/troubleshooting.html#log-files)

10-13 18:13:45:075 4045 OCC::ownCloudGui::slotOpenSettingsDialog: No configured folders yet, starting setup wizard
10-13 18:13:45:089 4045 OCC::OwncloudWizard::slotCurrentPageChanged: Current Wizard page changed to  0

When reproducing the steps above

2. Web server error log:

3. Server logfile: nextcloud log (data/nextcloud.log):