Resolves: rhbz#1673198 cannot overwrite open file with export

this reverts

commit 3c4cfa20
Date:   Mon Nov 26 12:51:05 2007 +0000

    INTEGRATION: CWS fwk72 (1.195.14); FILE MERGED
    2007/09/10 14:55:01 mav 1.195.14.1: #i81437# do not allow to export to the file the document is based on

Change-Id: I8bf1524a8cc2d6d1911bdd228f33f1b7723e1d6e
Reviewed-on: https://gerrit.libreoffice.org/67491
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>