Cannot edit citations if they appear at the end of a table cell

[adomasven]

Report: https://forums.zotero.org/discussion/89961/cannot-read-property-startswith-of-null

Occurs due to the way we try to move the cursor out of the citation by opening and closing the link editing dialog and then issuing <ArrowRight> keyboard event. Not entirely sure how to address this, but the move to canvas rendering might change this behavior anyway.