Handle dispatch() directly during event handling

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.

src/common/communication.h

@@ -364,7 +364,7 @@ class EventHandler {
         // `next_plugin_id` in `GroupBridge`
         std::map<size_t, std::jthread> active_secondary_requests{};
         std::atomic_size_t next_request_id{};
-        std::mutex active_secondary_requests_mutex;
+        std::mutex active_secondary_requests_mutex{};
         accept_requests(
             *acceptor, logging,
             [&](boost::asio::local::stream_protocol::socket secondary_socket) {