s3: smbd - Prevent file truncation on an open that fails with share mode violation.

s3: smbd - Prevent file truncation on an open that fails with share mode violation.

Fix from Volker, really - just tidied up a little.
The S_ISFIFO check may not be strictly neccessary,
but doesn't hurt (might make the code a bit more complex
than it needs to be).

Fixes bug #10671 - Samba file corruption as a result of failed lock check.

https://bugzilla.samba.org/show_bug.cgi?id=10671

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>