A couple of new user gender related fixes

- Default gender of ' ' (instead of '')
- Don't write the gender to the user's birthdate

webv4/root/api/register.ssjs

@@ -141,7 +141,7 @@ if (valid_param('phone', MIN_PHONE, LEN_PHONE)) {
 }
 
 if (valid_param('gender', 1, 1) && ['X', 'M', 'F', 'O'].indexOf(request.get_param('gender')) > -1) {
-	prepUser.birthdate = clean_param('gender');
+	prepUser.gender = clean_param('gender');
 } else if (required(UQ_SEX)) {
 	reply.errors.push(locale.strings.api_register.error_invalid_gender);
 }