Add a workaround for a bug in Ardour 5.X

Ardour will send events to the plugin before it has even finished
initializing. This has been fixed back in 2018 but Ardour has not seen a
stable release since then.

https://tracker.ardour.org/view.php?id=7668

README.md

@@ -10,18 +10,17 @@ also staying easy to debug and maintain.
 
 There are a few things that should be done before releasing this, including:
 
-- Do some final refactoring/clean up. There are a few small todos left for
-  things that could be a made little bit prettier.
 - Add missing details if any to the architecture section.
 - Rewrite parts of this readme.
 - Briefly verify that this also works fine in Reaper and Ardour.
 
 ## Tested with
 
-yabridge has been primarily tested under and verified to work correctly with:
+Yabridge has been verified to work correctly with:
 
 - Bitwig Studio 3.1 and the beta releases of 3.2
 - Carla 2.1
+- Ardour 5.12
 - Wine Staging 5.5 and 5.6 (the wine-staging-5.7-1 package currently in Arch and
   Manjaro's repositories is broken because of a regression in application
   startup behavior)
@@ -70,8 +69,8 @@ find "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins" -type f -iname '*.
 ### Copying
 
 It is also possible to use yabridge by creating copies of `libyabridge.so`
-instead of making symlinks. This is not recommended as it makes updating a
-hassle, but it may be required if your host has issues using symlinks. If you
+instead of making symlinks. This is not recommended as it makes updating more
+difficult, but it may be required if your host has issues using symlinks. If you
 choose to do this, then you'll have to make sure `yabridge-host.exe` and
 `yabridge-host.exe.so` are somewhere in your search path as otherwise yabridge
 won't be able to find them. Either copy them to `/usr/local/bin` (not

src/plugin/host-bridge.cpp

@@ -330,6 +330,22 @@ intptr_t HostBridge::dispatch(AEffect* /*plugin*/,
                               intptr_t value,
                               void* data,
                               float option) {
+    // HACK: Ardour 5.X has a bug in its VST implementation where it calls the
+    //       plugin's dispatcher before the plugin has even finished
+    //       initializing. This has been fixed back in 2018, but there has not
+    //       been a release that contains the fix yet. This should be removed
+    //       once Ardour 6.0 gets released.
+    //       https://tracker.ardour.org/view.php?id=7668
+    if (BOOST_UNLIKELY(plugin.magic == 0)) {
+        logger.log_event(true, opcode, index, value, nullptr, option);
+        logger.log(
+            "   WARNING: The host has dispatched an event before the plugin "
+            "has finished initializing, ignoring the event. (are we running "
+            "Ardour 5.X?)");
+        logger.log_event_response(true, opcode, 0, nullptr);
+        return 0;
+    }
+
     DispatchDataConverter converter(chunk_data, editor_rectangle);
 
     switch (opcode) {