commit 68c32f9c upstream.

Make sure to check the number of endpoints to avoid dereferencing a
NULL-pointer should a malicious device lack endpoints.

Fixes: cf7776dc ("[PATCH] isdn4linux: Siemens Gigaset drivers -
direct USB connection")
Cc: Hansjoerg Lipp <hjlipp@web.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>