It was forgotten to add `-f` (force) option for `ln` in
95687867d1. This enables opening files
with the same names, but different contents, with a new NeoMutt
instance, after the previous is closed.

In the latest neomutt release (2022-04-08), neomutt/neomutt/pull/3267 is
merged. Neomutt doesn't overwrite files with zeros on closing anymore,
just unlinks it. Therefore, instead of copying, files can be hard
linked.

* Simple Fixes

* Tweak wording

* Update openfile

* ShellChecked

* Little Fixes