Using VST3 plug-ins with OpenMPT development

[Saga Musix]

Ah, I see now what the issue is; there's a cache flag that OpenMPT uses to determine whether a plugin is an instrument that was only updated once for the shell itself, but if the plugins inside the shell reported something different, it was not updated anymore. In this particular case, the shell plugin didn't claim to be an instrument plugin. r21525 should fix this issue. For plugins already loaded into OpenMPT's list of known plugins, the display can be fixed by inserting the plugin into a song - or you can remove the plugins from the list to force a rescan.