Set the default host api in PortaudioBackend when initializing portaudio

Not setting a default driver causes issues with the EngineControl dialog

libs/backends/portaudio/portaudio_io.cc

@@ -321,6 +321,8 @@ PortAudioIO::initialize_pa ()
 			return false;
 		}
 		_initialized = true;
+		_host_api_index = Pa_GetDefaultHostApi ();
+		_host_api_name = get_host_api_name_from_index (_host_api_index);
 	}
 
 	return true;
@@ -343,6 +345,14 @@ PortAudioIO::host_api_list (std::vector<std::string>& api_list)
 	}
 }
 
+std::string
+PortAudioIO::get_host_api_name_from_index (PaHostApiIndex index)
+{
+	std::vector<std::string> api_list;
+	host_api_list(api_list);
+	return api_list[index];
+}
+
 bool
 PortAudioIO::set_host_api (const std::string& host_api_name)
 {

libs/backends/portaudio/portaudio_io.h

@@ -98,6 +98,7 @@ private: // Methods
 	void clear_device_lists ();
 	void add_default_devices ();
 	void add_devices ();
+	std::string get_host_api_name_from_index (PaHostApiIndex index);
 
 private: // Data
 	int  _state;