Add IUnitHandler stubs to component handler proxy

src/common/serialization/vst3/component-handler-proxy.h

@@ -18,6 +18,7 @@
 
 #include "../common.h"
 #include "component-handler/component-handler.h"
+#include "component-handler/unit-handler.h"
 
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
@@ -30,7 +31,8 @@
  * by the plugin we are proxying for the `IComponentHandler*` argument passed to
  * plugin by the host.
  */
-class Vst3ComponentHandlerProxy : public YaComponentHandler {
+class Vst3ComponentHandlerProxy : public YaComponentHandler,
+                                  public YaUnitHandler {
    public:
     /**
      * These are the arguments for constructing a
@@ -55,11 +57,13 @@ class Vst3ComponentHandlerProxy : public YaComponentHandler {
         native_size_t owner_instance_id;
 
         YaComponentHandler::ConstructArgs component_handler_args;
+        YaUnitHandler::ConstructArgs unit_handler_args;
 
         template <typename S>
         void serialize(S& s) {
             s.value8b(owner_instance_id);
             s.object(component_handler_args);
+            s.object(unit_handler_args);
         }
     };