XWIKI-20454: Client side mimetype restriction check does not take into account the right document

Fix webstandards validation issue.

xwiki-platform-core/xwiki-platform-attachment/xwiki-platform-attachment-validation/xwiki-platform-attachment-validation-ui/src/main/resources/XWiki/Attachment/Validation/Code/MimetypeValidation.xml

@@ -36,11 +36,13 @@
   <minorEdit>false</minorEdit>
   <syntaxId>xwiki/2.1</syntaxId>
   <hidden>true</hidden>
-  <content>{{velocity wiki='false'}}
+  <content>{{velocity wiki="false"}}
+#if ($request.documentReference)
 $jsontool.serialize({
-  "allowedMimetypes": $services.attachmentValidation.getAllowedMimetypes($!request.documentReference),
-  "blockerMimetypes": $services.attachmentValidation.getBlockerMimetypes($!request.documentReference)
+  "allowedMimetypes": $services.attachmentValidation.getAllowedMimetypes($request.documentReference),
+  "blockerMimetypes": $services.attachmentValidation.getBlockerMimetypes($request.documentReference)
 })
+#end
 {{/velocity}}</content>
   <object>
     <name>XWiki.Attachment.Validation.Code.MimetypeValidation</name>