R1:dde63af1cc86

Fix a JS console warning when hovering over replies to ghosts on lines which no longer exist

Summary:
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.

Test Plan:
- Wrote `long.txt`.
- Created revision.
- Added an inline near the…