Fix NULL dereference when there are no directory vshortcuts defined

As reported by Accession in #synchronet at irc.synchro.net

src/sbbs3/websrvr.c

@@ -3365,6 +3365,7 @@ static void add_vshortcuts()
 			break;
 		count++;
 	}
+	if(alias_list != NULL)
 		alias_list[count] = NULL;	/* terminate list */
 }