Let group hosts shut down on their own if unused

We would never try to shut the group host down if nothing ever tried to
connect to it. This could happen when the native host gets killed after
initializing the yabridge plugin but before it gets the chance to
request the group host process to host a plugin.

CHANGELOG.md

@@ -81,6 +81,10 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   plugins. We now explicitly reparent the window to back the root window first
   before deferring the window closing. This should fix the issue, while still
   keeping editor closing nice and snappy.
+- Allow plugin group host processes to shut down by themselves if it doesn't get
+  a request to host any plugins. This can happen when the DAW gets killed after
+  starting the group host process but before the native yabridge plugins
+  requests the group host process to host a plugin.
 - Prevented latency introducing plugins VST3 from causing **Ardour** and
   **Mixbus** to freeze when loading the plugin. This for example prevents
   _Neural DSP Darkglass_ from freezing when used under those DAWs.