Call smb_updatethread() from sbbs_t::email() to perform Keyop "magic"
As discovered by Keyop and reported via IRC, when replying *to* a local mail box and *not* using the hard-coded email menu (e.g. when when using msglist.js), the original message's "Replied" attribute flag was not set. When replying to a netmail address (at least, Internet or FidoNet, unsure about QWKnetmail), the attribute would be set. This discrepancy was because this email() function doesn't use the "modern" smb_addmsg() function (which also calls smb_updatethread()), but add the message body text the old/manual way and never called smb_updatethread(). smb_updatethread() does the thread linkage stuff (which is usually unnoticed in the mail base) *and* sets the "Replied" attribute of the original message, if it's not already set. This function should be overhauled to use smb_addmsg(), but this 2-line change at least addresses this issue for now. There's probably other places (e.g. importing mail replies via QWK/REP packets) where this thread-linkage and "Replied" attribute flag setting is still not happening.