Fix serializing VST2 speaker arrangements

CHANGELOG.md

@@ -6,6 +6,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic
 Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- Fixed VST2 speaker arrangement configurations returned by the plugin not being
+  serialized correctly. No plugins seem to actually use these, so it should not
+  have caused any issues.
+
 ## [3.3.1] - 2021-06-09
 
 ### Added

src/common/serialization/vst2.h

@@ -507,8 +507,8 @@ void serialize(S& s, Vst2EventResult::Payload& payload) {
                   s.container1b(chunk.buffer, binary_buffer_size);
               },
               [](S& s, AEffect& effect) { s.object(effect); },
-              [&](DynamicSpeakerArrangement& speaker_arrangement) -> void* {
-                  return &speaker_arrangement.as_c_speaker_arrangement();
+              [](S& s, DynamicSpeakerArrangement& speaker_arrangement) {
+                  s.object(speaker_arrangement);
               },
               [](S& s, VstIOProperties& props) { s.object(props); },
               [](S& s, VstMidiKeyName& key_name) { s.object(key_name); },