Fixes T11662. In the very obscure situation described in that task, quiet a JS console warning.

The actual edit operation appears to work correctly after changes elsewhere.

There aren't really any legitimate lines for us to highlight in this case so I'm just giving up rather than trying to do something approximate.

• Wrote long.txt.
• Created revision.
• Added an inline near the bottom.
• Removed most of long.txt.
• Updated revsion.
• Replied to the ghost inline.
• Edited the reply to the ghost inline, worked.
• Hovered the reply to the ghost inline: no line highlight, but no errors.