Check if an user or group id is blank before getting the related information

UserSuggestionActionsBean#getUserInfo calls userManager.getGroup(id) without testing if the id is empty. This causes a warning in the logs, which could be avoided

WARN  [LDAPSession] The application should not query for entries with an empty id => return no results

The above method getPrefixedUserInfo does this check before going on

        if (!StringUtils.isBlank(id)) {