RTAS assert in MessageManager

hi, with the latest tip when closing the JucePlugin there is an assert in MessageManager

// If you hit this assertion, then you've probably leaked a Component or some other
// kind of MessageListener object...
jassert (messageListeners.size() == 0);

the debugger shows that there’s still 1 MessageListener of type internalAsyncHandler

Ah yes, that’s just the process object itself. Nothing to worry about, but I’ll tidy it up to avoid the assertion.