Fix messages between directly connecting objects

iZotope plugins will already send messages when connect() is called on
the first object, so this flag has to be set on both host contexts at
the same time.

src/wine-host/bridges/vst3-impls/host-context-proxy.cpp

@@ -62,7 +62,7 @@ Vst3HostContextProxyImpl::createInstance(Steinberg::TUID /*cid*/,
     // Class IDs don't have a meaning here, they just mirrored the interface
     // from `IPlugFactory::createInstance()`
     constexpr size_t uid_size = sizeof(Steinberg::TUID);
-    if (!_iid || strnlen(_iid, uid_size) < uid_size) {
+    if (!_iid || !obj || strnlen(_iid, uid_size) < uid_size) {
         return Steinberg::kInvalidArgument;
     }
 
@@ -98,6 +98,8 @@ Vst3HostContextProxyImpl::createInstance(Steinberg::TUID /*cid*/,
                "IHostApplication::createInstance() for indirectly "
                "connected objects has not yet been implemented"
             << std::endl;
+
+        *obj = nullptr;
         return Steinberg::kNotImplemented;
     }
 }