Fix denial of service - memory corruption.

Fix denial of service - memory corruption.

CVE-2011-0719

Fix bug #7949 (DoS in Winbind and smbd with many file descriptors open).

All current released versions of Samba are vulnerable to
a denial of service caused by memory corruption. Range
checks on file descriptors being used in the FD_SET macro
were not present allowing stack corruption. This can cause
the Samba code to crash or to loop attempting to select
on a bad file descriptor set.

A connection to a file share, or a local account is needed
to exploit this problem, either authenticated or unauthenticated
(guest connection).

Currently we do not believe this flaw is exploitable
beyond a crash or causing the code to loop, but on the
advice of our security reviewers we are releasing fixes
in case an exploit is discovered at a later date.
(cherry picked from commit c3ad6eb506623435d3d9ce62d6f34ed1c960d4be)