The signature is shown by default when sending a mail and in particular
case it is not shown.
In c8d283a592 there was a small regression that in some instance the
signature that was shown before is not shown anymore. This is because
the default in those instance is to not show signature.
eg. a message sent in a chatter would not have signature in sent emails
With this commit, the previous behavior is reintroduced.
opw-1903001
opw-1896262
closes#29088