mac-capture: Fix bug where audio device couldn't be changed

If the user selected the "default" device for audio capture on mac, it
would no longer be able to be switched to another device due to the
"default_device" variable being set.

plugins/mac-capture/mac-audio.c

@@ -89,6 +89,9 @@ static bool find_device_id_by_uid(struct coreaudio_data *ca)
 	if (!ca->device_uid)
 		ca->device_uid = bstrdup("default");
 
+	ca->default_device = false;
+	ca->no_devices = false;
+
 	/* have to do this because mac output devices don't actually exist */
 	if (astrcmpi(ca->device_uid, "default") == 0) {
 		if (ca->input) {