Section field loses choices after AJAX action

The steps to reproduce this error seem convoluted but occur in practice when our users use AJAX funtionality in node forms with the oa_section_ref field.

1. Edit a node that is part of a space to which the user only has admin access.
2. This means that 'target group' contains the space in 'other groups' and nothing in 'your groups'.
3. When the form loads, the Section selection list is populated via a query that is modified by oa_sections_query_entityreference_alter()
4. This function uses _oa_sections_get_current_selected_space() to find the current space of the entity. As this is the initial load, the space is read from the entity itself.
5. When some AJAX action is triggered, such as clicking 'Add another item' below the 'Other Groups' field, the Sections field is repopulated in this AJAX callback.
6. Again, oa_sections_query_entityreference_alter() and _oa_sections_get_current_selected_space() are invoked.
7. Now, the following branch in _oa_sections_get_current_selected_space() is triggered:
   

     if (isset($_POST['og_group_ref'])) {
       $process = $_POST['og_group_ref'];
     }
   

   As this is now a POST request.

8. When the user is not member of the space but has administrative access, the contents of $_POST['og_group_ref']
   are like this:
   ['und' => [['default' => '', 'admin' => 'Group (123)']]]
9. Somewhere further along this function, only $process[LANGUAGE_NONE][0]['default'] is checked and $process[LANGUAGE_NONE][0]['admin'] is ignored.
10. Because of this, the code assumes there is no space associated with the node.
11. oa_sections_query_entityreference_alter() now adds $query->condition('1', '0', '='); to the query and the Sections option list is populated with 0 choices (except '- None -').

The bug can be easily fixed by also checking $process[LANGUAGE_NONE][0]['admin'].