if no mech have no session, its ok, just don't call it.

git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@21225 ec53bebd-3082-4978-b11e-865c3cabbd6b

appl/ftp/ftp/security.c

@@ -586,7 +586,7 @@ sec_userok(char *userstr)
 int
 sec_session(char *user)
 {
-    if(sec_complete)
+    if(sec_complete && mech->session)
 	return (*mech->session)(app_data, user);
     return 0;
 }