Potential bug in /inc/core-form.php

Thanks to Jeff Starr for a handy and functional plugin.

With debug enabled, I noticed errors like:

PHP Warning: Invalid argument supplied for foreach() in /var/www/domain.com/htdocs/wp-content/plugins/contact-form-x/inc/core-form.php on line 45

There might be a bug here, because on line 41 $fields variable might be set to null. But on line 45, always, even if $fields is null, the plugin tries to call foreach($fields as $id => $field).

I suggest replacing:

$fields = isset($options_form['display-fields']) ? $options_form['display-fields'] : null;

on the:

$fields = isset($options_form['display-fields']) ? $options_form['display-fields'] : array();

Then the foreach() will always get an array.