"Show full file" does not allow commenting on expanded lines

Steps to reproduce

• open merge request where part of the diff is collapsed
• click "Show full file" button
• try to comment on a line that is not changed

Example Project

!16857 (diffs)

What is the current bug behavior?

No comment form is shown, error in the browser console:

Screen_Recording_2019-09-17_at_10.45.12

TypeError: "r.highlighted_diff_lines.find(...) is undefined"

in TOGGLE_LINE_HAS_FORM mutation

What is the expected correct behavior?

comment form is shown