Select Portaudio as the default sound system if ALSA is not compiled in.

diff --git a/src/lingot-config.c b/src/lingot-config.c
index dd4bf65..29c3c9b 100644
--- a/src/lingot-config.c
+++ b/src/lingot-config.c
@@ -429,7 +429,11 @@ void lingot_config_load(LingotConfig* config, char* filename) {
 				*((audio_system_t*) param) = str_to_audio_system_t(
 						char_buffer_pointer);
 				if (*((audio_system_t*) param) == (audio_system_t) -1) {
+# ifdef ALSA
 					*((audio_system_t*) param) = AUDIO_SYSTEM_ALSA;
+# elif PORTAUDIO
+					*((audio_system_t*) param) = AUDIO_SYSTEM_PORTAUDIO;
+# endif
 					char buff[1000];
 					sprintf(
 							buff,