Wrong diff highlighting for "no newline at end of file"

When a file without newline at the end is "fixed" by adding a newline, the diff view shows the message "\ No newline at end of file" in green:


This is a bit misleading, it suggests that the change was to remove the newline rather than add it.

For comparison here's how it looks with the default `git diff`:


(tested on gitui 0.26.1)

Reproduce the reported diff view behavior for a file whose missing final newline is added, using the issue screenshots and gitui 0.26.1 as reference. Trace the diff highlighting behavior and verify that the no-newline message is colored consistently with the corresponding default git diff output.

Scritto dal modello di indicizzazione a partire dal testo della issue.