Rename autoresolveCheck to autosecureCheck

* src/mail.cpp, src/mail.h (Mail::autoresolveCheck): Rename
to autosecureCheck.
(Mail::autsecureCheck): Also check for opt.autosecure.

This reduces confusing naming and ensures that when opt.autosecure
is not set auto secure won't happen.

(cherry picked from commit 3b770f928eb17fd876a00e85e7b384d566de2175)

• GnuPG-Bug-Id: T4126