When clicking in a single-file diff view to enter staging (or custom patch
editing, when coming from the commit files panel), and then pressing shift-down
or shift-up to select a range, it would move the selected line rather than
creating a range. Only on the next press would it start to select a range from
there.
This is very similar to the fix we made for pressing escape in 0e4d266a52.
a58770ee1b