Prevent out of boundary write with configuration files in which too many

quoted arguments are stored for other window managers.

The quotation handling happens within the while loop without checking if
the "end" limit has been already reached. If this happens, the final
NULL assignment leads to an out of boundary write on stack.

OK okan@

util.c

@@ -53,7 +53,7 @@ u_exec(char *argstr)
 {
 #define MAXARGLEN 20
 	char	*args[MAXARGLEN], **ap = args;
-	char	**end = &args[MAXARGLEN - 1], *tmp;
+	char	**end = &args[MAXARGLEN - 2], *tmp;
 	char	*s = argstr;
 
 	while (ap < end && (*ap = strsep(&argstr, " \t")) != NULL) {