[web/views/rdf] Take the second element of XY equivalent for non final relation
When given a Yams snippet of the form `<etype> <rtype>` ``xy.xeq()`` will
return the XML snippet equivalent to this relation in the form of a tuple
`(subject, rtype, object)` so ``item`` will always be a tuple here.
In fact, the correct code appears just a few lines above (around line 88) for
final relations so I guess this is a copy-paste mistake.
Closes #4745929.
<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>