s3: smbd: filenames - ensure we replace the missing '/' if we error in an intermediat...

s3: smbd: filenames - ensure we replace the missing '/' if we error in an intermediate POSIX path.

Previous regression test ensures we still return the correct
error code for POSIX pathname operations.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13803

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Mon Feb 25 09:33:27 CET 2019 on sn-devel-144

(cherry picked from commit 3f1a13a94a753c5cb3b9f2cf795df5adb0f74205)