"Keep plugin on top when not embedded" fails to apply to native Linux VST .so files

### Bug Summary
"Keep plugin on top when not embedded" fails to apply to native Linux VST .so files

#### Steps to reproduce
Enable "Keep plugin on top when not embedded" in settings. Restart LMMS for changes to take effect. Load .so VST instrument or plugin. Click anywhere besides within the plugin.

#### Expected behavior
Plugin stays on top.

#### Actual behavior
Plugin does not stay on top.

#### Screenshot
https://github.com/LMMS/lmms/assets/65249472/35d637dc-daa4-431e-80ea-2a149ea3d5b8

#### Affected LMMS versions
All that support loading .so files.

#### Logs
```
Starting detached.
unique ID: Vita
RemotePlugin::DebugMessage: inputs: 0 output: 2
RemotePlugin::DebugMessage: creating editor
RemotePlugin::DebugMessage: editor successfully created
RemotePlugin::DebugMessage: plugin name: Vital
RemotePlugin::DebugMessage: initialization done
```

No source files or tests are named. Reproduce the issue by enabling "Keep plugin on top when not embedded," restarting LMMS, and loading a native Linux VST .so plugin; trace the detached plugin window handling. Done means the plugin remains on top after clicking outside it.

Written by the indexing model from the issue text.