Flush the bus info cache in more places

The current approach 'works', but better err on the safe side. Once this
caching layer is no longer necessary we should just remove it.

src/plugin/bridges/vst3-impls/plugin-proxy.cpp

@@ -63,6 +63,12 @@ bool Vst3PluginProxyImpl::unregister_context_menu(size_t context_menu_id) {
     return context_menus.erase(context_menu_id);
 }
 
+void Vst3PluginProxyImpl::clear_bus_cache() {
+    if (processing_bus_cache) {
+        processing_bus_cache.emplace();
+    }
+}
+
 tresult PLUGIN_API Vst3PluginProxyImpl::setAudioPresentationLatencySamples(
     Steinberg::Vst::BusDirection dir,
     int32 busIndex,
@@ -80,6 +86,8 @@ tresult PLUGIN_API Vst3PluginProxyImpl::setBusArrangements(
     int32 numIns,
     Steinberg::Vst::SpeakerArrangement* outputs,
     int32 numOuts) {
+    clear_bus_cache();
+
     // NOTE: Ardour passes a null pointer when `numIns` or `numOuts` is 0, so we
     //       need to work around that
     return bridge.send_audio_processor_message(
@@ -311,20 +319,11 @@ Vst3PluginProxyImpl::activateBus(Steinberg::Vst::MediaType type,
 
 tresult PLUGIN_API Vst3PluginProxyImpl::setActive(TBool state) {
     // HACK: Even though we have implemented this cache specifically for REAPER,
-    //       REAPER mixes up `IComponent::setActive` and
-    //       `IAudioProcessor::setProcessing`. `IAudioProcessor::setProcessing`
-    //       is called before setting up bus arrangements, so without this the
-    //       cache would be filled with default data rather than the bus
-    //       arrangement chosen by REAPER. So now our workaround to get
-    //       acceptable performance in REAPER needs a workaround of its ownn.
-    //       Great!
-    // TODO: We probably also need a reset on
-    //       `IComponentHandler::restartComponent()`
-    if (state) {
-        processing_bus_cache.emplace();
-    } else {
-        processing_bus_cache.reset();
-    }
+    //       REAPER doesn't use `IComponent::setProcessing` properly and calls
+    //       it before doing setting up input and output busses. So now our
+    //       workaround to get acceptable performance in REAPER needs a
+    //       workaround of its ownn.  Great!
+    clear_bus_cache();
 
     return bridge.send_audio_processor_message(
         YaComponent::SetActive{.instance_id = instance_id(), .state = state});