This will require more testing of course, but I think it should be safe.
This would increase the potential maximal throughput in group hosts
significantly.
std::function does not allow non-movable lambdas, so capturing by move
doesn't work there. And the old solution of course has issues with
dangling pointers (but because this is C++ the compiler still thinks
it's A-Ok).
When the message loop is active and we get an incoming dispatch() event,
we'll just handle it directly. In practice this would only be needed
when the event is a response to an `audioMaster()` call made during the
event loop, but we can't know that. This allows the `getProgram()`
during `audioMasterUpdateDisplay()` in REAPER and Renoise to work
correctly. Hopefully this doesn't cause random rare breakage.
Robbert van der Helm