smbd: Fix open_pathref_base_fsp()'s implicit conn_cwd assumption

smbd: Fix open_pathref_base_fsp()'s implicit conn_cwd assumption

Opening a stream base file only worked if "dirfsp == conn->cwd_fsp":
We have replaced fsp->fsp_name with the full dirfsp->relative pathname
at the point where open_pathref_base_fsp() is called. In case dirfsp
is already a subdirectory in a share, this breaks because the
open_pathref_base_fsp() uses fsp->fsp_name, not the original
dirfsp-relative one.

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