Upload tab displayed in image dialog even if user cannot upload

Reproduction steps:

• Edit CKEditor.EditSheet first JavaScript Object to set:

  var uploadDisabled = true; //element.hasAttribute('data-upload-disabled');
  

• Start editing a page and open the image dialog

Expected result:

• the upload tab shouldn't be displayed

Obtained result:

• the upload tab is displayed
• an error appears when trying to upload an image