fix(container): fixing the rights check

[stonebuzz]

Since release 1.12.1 a bug appears from this PR #425

From Dictionnay Software form, it's impossible to add a criteria.
With super-admin profile it's OK

But with another profile and good right

It's impossible

The "Add" button disappear.

When plugin it's called from this hook

 $PLUGIN_HOOKS['post_item_form']['fields'] = ['PluginFieldsField',  'showForTab'];

the plugin tries to find a container for the object being viewed (RuleCriteria in this case)

The hook is called from CommonDBTM.class.php

1. Here canEdit return true
2. Here (after hook) can Edit return false

When plugin try to find a container related to the object this line break the check process (canEdit)

Here we can check directly the arg (instead of load object), because arg is determined by get_class function (which use an object)