[web/views] avoid propagation of NoSelectableObject in some case of inlined relations / permissions
When selecting an inlined creation form, we should catch the
NoSelectable exception that will be raised if the user cannot add
entities of the target type (this is not and cannot be verified earlier)
or if some other custom selector prevents the form from being selected.
Closes #6510921
<table class="attributeForm" style="width:100%;"
tal:attributes="id tab_id | nothing;
class tab_class | nothing;">
<tr tal:iter="widget lines">
<th class="labelCol" tal:content="structure python:widget.render_label(entity)">attrname</th>
<td tal:define="error python:widget.render_error(entity)" style="width:100%;"
tal:attributes="class python:error and 'error' or nothing">
<div tal:replace="structure error">error message if any</div>
<div tal:replace="structure python:widget.edit_render(entity)" >widget (input, textarea, etc.)</div>
<div tal:replace="structure python:widget.render_help(entity)">format help if any</div>
</td>
</tr>
</table>