Links wrapping images are removed on re-edit

Reproduction steps:

• create document with a link containing an image (for instance [[[[image:Help.Applications.Contributors.Charlie Chaplin@Charlie_Chaplin_portrait.png]]>>doc:]])
• save and view the page
• edit it again with ckeditor
• save

Expected result:

• the image an the link are preserved

Actual result:

• the link wrapping the image is removed

Notes:

• affect version to be refined
• might be linked to XWIKI-20850
• note reproduce on 15.2-rc-1