[QA] Comments added with richdocuments are rendered broken

[jnweiger]

Seen while testing richdocuments 3.0.0 rc.2 on server 10.11.0

• Add a comment via richdocuments to a pdf.
• open the pdf in owncloud's pdfviewer
• The rendering shows raw markup and a broken thumbnail

(left google chrome, right firefox)

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When downloaded, and viewed with the stock Ubuntu pdfviewser the comment renders fine: