[PATCH] Overrun in isdn_tty.c

This fixes coverity bug id #1237.  After the while loop, it is possible for
i == ISDN_LMSNLEN.  If this happens the terminating '\0' is written after
the end of the array.

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>