output/wasapi: implement Cancel()

src/output/plugins/wasapi/WasapiOutputPlugin.cxx

@@ -258,6 +258,7 @@ public:
 	std::chrono::steady_clock::duration Delay() const noexcept override;
 	size_t Play(const void *chunk, size_t size) override;
 	void Drain() override;
+	void Cancel() noexcept override;
 	bool Pause() override;
 	void Interrupt() noexcept override;
 
@@ -664,6 +665,14 @@ WasapiOutput::Drain()
 	thread->CheckException();
 }
 
+void
+WasapiOutput::Cancel() noexcept
+{
+	assert(thread);
+
+	thread->spsc_buffer.consume_all([](auto &&) {});
+}
+
 /// run inside COMWorkerThread
 void
 WasapiOutput::OpenDevice()