Initialize Portaudio device name (with an empty string for now).

diff --git a/src/lingot-config.c b/src/lingot-config.c
index 8d57596..dd4bf65 100644
--- a/src/lingot-config.c
+++ b/src/lingot-config.c
@@ -100,6 +100,7 @@ void lingot_config_restore_default_values(LingotConfig* config) {
 	config->audio_system = AUDIO_SYSTEM_ALSA;
 	sprintf(config->audio_dev[AUDIO_SYSTEM_OSS], "%s", "/dev/dsp");
 	sprintf(config->audio_dev[AUDIO_SYSTEM_ALSA], "%s", "plughw:0");
+	sprintf(config->audio_dev[AUDIO_SYSTEM_PORTAUDIO], "%s", "");

 	config->sample_rate = 44100; // Hz
 	config->oversampling = 25;