Plugin not working on first install

[fabienlege]

1. Install the plugin for the first time (fresh wordpress install)
2. Go to Settings > Restric taxonomies
3. Just check a category under "Roles" section and save settings
4. Datas was not saved and you get a warning in php error log :
   array_replace_recursive(): Argument #1 is not an array in /Users/arnaud/Sites/decideurs/wp-content/plugins/Restrict-Taxonomies-master/restrict-taxonomies.php on line 387

To bypass this problem, you need to click on "Reset config" and retry the procedure.
After a reset setting, plugin seem to work as expected.

Its seem that $options var contain empty string before user reset settings