[Bug]: Autostart failing due to existence of old kdsingleapp lock file

### ⚠️ Before submitting, please verify the following: ⚠️

- [x] This is a **bug**, not a question or a configuration issue.
- [x] This issue is **not** already reported on Github (I've searched it).
- [x] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

With the latest version 33 the nextcloud desktop client isn't starting because it appears that it is being blocked by an old lock file.

In testing this bug I've found that either performing a cold boot or removing the kdsingleapp lock file allows the client to start on the next session. The issue doesn't exist in version 4.0.8.

So far i've been able to reproduce on the following distros all with the Gnome desktop:
- Fedora Silverblue 43
- Fedora Workstation 43
- Debian 13
- Debian Sid

Previously reported here - https://github.com/flathub/com.nextcloud.desktopclient.nextcloud/issues/243 but was directed to open the bug upstream.

### Steps to reproduce

1. Install the flatpak version of the desktop client
2. Run the setup wizard and after initial sync verify that autostart is setup
3. log out and back in
4. The app will never autostart and any attempt to start will show the error "already running" but `flatpak ps` shows no running instance

### Expected behavior

Desktop client should autostart correctly

### Which files are affected by this bug

kdsingleapp

### Operating system

Linux

### Which version of the operating system you are running.

Fedora Silverblue 43, Fedora Workstation 43, Debian 13, Debian Sid

### Package

Community FlatPak

### Nextcloud Server version

32.0.6

### Nextcloud Desktop Client version

33.0.0

### Is this bug present after an update or on a fresh install?

Updated to a major version (ex. 3.16.3 to 3.17.0)

### Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

### Are you using an external user-backend?

- [x] Default internal user-backend
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell

```

### Additional info

_No response_