s3: libsmb: Fix use-after-free when accessing pointer *p.

s3: libsmb: Fix use-after-free when accessing pointer *p.

talloc_asprintf_append() might call realloc()
and therefore move the memory address of "path".

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12927

Signed-off-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Böhme <slow@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Jul 22 22:45:05 CEST 2017 on sn-devel-144

(cherry picked from commit 890137cffedcaf88a9ff808c01335ee14fcfd8da)

Autobuild-User(v4-5-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-5-test): Mon Jul 24 06:24:58 CEST 2017 on sn-devel-144