Fix deprecated method call

Hi-

I am having an intermittent issue with the nm-wp-login shortcode. If I put it on page to render a sign in form the page does not always redirect properly. If I got directly from the sign up success page to the sign in page in a brand new session(with chrome in incognito) logging in takes me to the log in page. it does not redirect me to the page I chose in settings. I am not sure what the root cause is but I did noticed a couple of warnings in the logs. First: get_currentuserinfo() /app/wp-content/plugins/wp-registration/classes/plugin.class.php:488 get_currentuserinfo() is deprecated and should be replaced with wp_get_current_user()

Second: in the nm_login_empty() function, the $user references nothing. Should this pull from the global $user variable and check to see if it is a wp_error instead?