Fix event handlers not being unregistered

This would cause crashes in Bitwig, as `RunLoopTasks`' destructor would
not be run after the event handler has been unregistered, and we
unregister the event handler in that destructor.

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

@@ -211,12 +211,12 @@ Vst3PlugViewProxyImpl::setFrame(Steinberg::IPlugFrame* frame) {
         // owned by REAPER then REAPER will eventually segfault We should thus
         // try to call those functions from an `IRunLoop` event handler.
         try {
-            run_loop_tasks = Steinberg::owned(new RunLoopTasks(plug_frame));
+            run_loop_tasks.emplace(plug_frame);
         } catch (const std::runtime_error& e) {
             // In case the host does not support `IRunLoop` or if we can't
             // register an event handler, we'll throw during `RunLoopTasks`'
             // constructor
-            run_loop_tasks = nullptr;
+            run_loop_tasks.reset();
 
             bridge.logger.log(
                 "The host does not support IRunLoop, falling back to naive GUI "

src/plugin/bridges/vst3-impls/plug-view-proxy.h

@@ -278,9 +278,7 @@ class Vst3PlugViewProxyImpl : public Vst3PlugViewProxy {
      * the host's GUI thread using a run loop event handler in
      * `Vst3PlugViewProxyImpl::run_gui_task`.
      *
-     * _This value is optional_ and it will this be a null pointer of the host
-     * does not support `IRunLoop`. We have to use an `IPtr` instead of a an
-     * `std::optional` in case the host also stores a pointer to this.
+     * This will be an `std::nullopt` if the hostdoes not support `IRunLoop`.
      */
-    Steinberg::IPtr<RunLoopTasks> run_loop_tasks;
+    std::optional<RunLoopTasks> run_loop_tasks;
 };