neomutt: apply patch to mitigate CVE-2020-28896
See https://github.com/neomutt/neomutt/releases/tag/20201120 &
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-28896 for
further information.
It seems as `neomutt` (and also `mutt`) had an improper handling of
broken IMAP connections and thus a risk of leaking sensitive
information. The relevant patch can be found at
https://github.com/neomutt/neomutt/commit/9c36717a3e2af1f2c1b7242035455ec8112b4b06
