Initialize sbbs_t::client and call client_on() as expected for logins

See sbbs_t::logon() for example

Note: the client.protocol is still "SSH" here (not "SFTP"). Perhaps that
should be changed?

Does any client actually support simultaneous "SSH" and "SFTP" sessions over
the same socket?

src/sbbs3/answer.cpp

@@ -427,6 +427,9 @@ bool sbbs_t::answer()
 								mouse_mode = MOUSE_MODE_OFF;
 								autoterm = 0;
 								sys_status |= SS_USERON;
+								SAFECOPY(client.user, useron.alias);
+								client.usernum = useron.number;
+								client_on(client_socket, &client,/* update: */TRUE);
 							}
 							else {
 								lprintf(LOG_NOTICE, "%04d Trying to create new user over sftp, disconnecting.", client_socket);