Client side mimetype restriction check does not take into account the right document

Following the same steps as XWIKI-20367:

• Create a page Test.XClass.WebHome containing a textarea property named "test" that uses WYSIWYG editor and Wiki Syntax
• Create a page Test.XObj.WebHome containing an xobject of type XClass previously created
• Create a page Test.Test containing the following piece of code:

  {{velocity}}
  #set ($myDoc = $xwiki.getDocument('Test.XObj.WebHome'))
  #set ($myObj = $myDoc.getObject('Test.XClass.WebHome'))
  $myObj.display('test', 'edit')
  {{/velocity}} 

Then add attachments mimetypes restrictions:

• allow image/* on XObj
• allow text/plain on Test

Upload an image usage the image dialog.

Expected:

• The image upload is accepts

Actual:

• The image upload is reject since the attachment restriction of the Test page are used instead of XObject