Enabling VFS with no VFS models installed segfaults the client #10174

⚠️ Before submitting, please verify the following: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I have searched for it).
• Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• I agree to follow Nextcloud's Code of Conduct

Bug description

Installing the Nextcloud desktop client on OpenSUSE Tumbleweed does not install the separate package nextcloud-desktop-vfs-plugin. If the user the reads about experimental support for VFS and enables the experimental option in the config file, trying to then enable it with just cause the desktop client to segfault with no indication as to why.

Steps to reproduce

1. zypper install nextcloud-desktop
2. vi ./config/Nextcloud/nextcloud.cfg - add showExperimentalOptions=true
3. Open the desktop client, click the three dots and choose "Enable virtual file sync".
4. core dump / segfault

Expected behavior

The cause is a dereferenced nullptr. Expecte behaviour would be to either silently fail or in the best case scenario notify the user that there are no VFS plugins installed.

Which files are affected by this bug

src/gui/guiutility.cpp

Operating system

Linux

Which version of the operating system you are running.

OpenSUSE Tumbleweed

Installation method

Distro package manager (please test with the AppImage package ?)

Nextcloud Server version

34.0.0

Nextcloud Desktop Client version

33.0.5daily

Did this occur after an update or on a clean installation?

Clean desktop client installation

Are you using the Nextcloud Server Encryption module?

No

Are you using an external user-backend?

• Default internal user-backend
• LDAP or Active Directory
• SSO - SAML
• Other

Nextcloud Server logs

Additional info

I'm intending to make a PR that fixes the crash after creating the issue.