Fix unix_convert() for "*" after changing map_nt_error_from_unix().

map_nt_error_from_unix() now assumes that it is called in
an error path and returns an error even for a given errno == 0.
The original behaviour of unix_convert() used the mapping
of errno == 0 ==> NT_STATUS_OK to return success through
an error path.

I think this must have been an oversight, and unix_convert() worked
only by coincidence (or because explicitly using the knowledge
of the conceptually wrong working of map_nt_error_from_unix().

This patch puts this straight by not interpreting errno == 0
as an error condition and proceeding in that case.

Jeremy - please check!

Michael
(This used to be commit ec5956ab0df1b3f567470b2481b73da9c3c67371)

source3/smbd/filename.c

@@ -477,7 +477,7 @@ NTSTATUS unix_convert(TALLOC_CTX *ctx,
 				}
 
 				/* ENOENT is the only valid error here. */
-				if (errno != ENOENT) {
+				if ((errno != 0) && (errno != ENOENT)) {
 					/*
 					 * ENOTDIR and ELOOP both map to
 					 * NT_STATUS_OBJECT_PATH_NOT_FOUND