net/samba411 net/samba412 net/samba413: Fix zero-sized VLAs

With recent versions of clang, samba could dump core shortly after
startup, terminating with either SIGILL or SIGSEGV.

Investigation showed that samba is using C99 variable length arrays
(VLAs), and in some cases the length of these arrays would become zero.
Since this is undefined behavior, various interesting things would
happen, often ending in segfaults.

Fix this by avoiding to use zero as the length for these VLA
declarations.

A similar patch was also sent upstream, and was accepted and included in
subsequent samba releases.

See also: https://bugzilla.samba.org/show_bug.cgi?id=14605

Reported by: Dries Michiels <driesm.michiels@gmail.com>
PR: 252157
MFH: 2021Q1