Locking of ExpFields is required to lock current state of fields and database cursor:
generation of print preview and some other operations can cause changing
of current database record, especially if document contains nextrecord fields.

Reviewed-on: https://gerrit.libreoffice.org/17857Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
(cherry picked from commit 959a5043)

Conflicts:
	sw/source/uibase/dbui/dbmgr.cxx

Change-Id: If0466ef2489d96264380b5978ef7d7cf3f545c23
Reviewed-on: https://gerrit.libreoffice.org/17877Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Katarina Behrens <Katarina.Behrens@cib.de>