Fix LocationError when trying to access a web site with absolute url

bt5/erp5_knowledge_pad/SkinTemplateItem/portal_skins/erp5_knowledge_pad/Base_viewKnowledgePadMacroLibrary.xml

@@ -148,7 +148,7 @@
   <div id="rename_tab_dialog" \n
        tal:condition="python:active_knowledge_pad is not None"\n
        class="toggable_dialog"\n
-       tal:define="active_knowledge_pad_relative_url active_knowledge_pad/getRelativeUrl">\n
+       tal:define="active_knowledge_pad_relative_url python:active_knowledge_pad and active_knowledge_pad.getRelativeUrl() or \'\'">\n
     <h3 i18n:translate="" i18n:domain="ui"> Rename tab </h3>\n
       <span i18n:translate="" i18n:domain="ui">Tab name</span>:\n
       <input type="text"\n