v1 of obs_properties_add_button will be deprecated soon.
Also fixes UNUSED_PARAMETER calls in the callbacks for parameters that
are not actually unused, and moves the other ones to the top (as in most
of the rest of the project).
The 6.4 runtime rely on Freedesktop 22.08 which provide a more recent
version of Mesa and PipeWire.
The switch to 22.08 also requires to migrate paths of VST 2 plugins.
A prior patch made the button to show/hide a VST check the current
status of a loaded VST. This lead to situation where upon first
selection a VST might be loaded but the button's visibility is not
changed.
This change will reevaluate the status of a loaded VST upon selection
in the drop-down menu and trigger button visibility accordingly.
This changes the buttons to better reflect the state of the filter:
* When no VST is loaded, hide both buttons
* Check if VST is loaded before changing visibility
* Check if VST is loaded and editor is open before changing visibility
Per OBS API documentation, `get_properties` can be used to get the
properties of a source, but also of a source type. The latter would
pass a NULL pointer for a given source.
This adds the necessary change to avoid crashing OBS by passing such
a null pointer.
