Test removal or not of escape char in number format strings in XLSX

Change-Id: I02a7e1bfd9df1ffd3bbad7dc072cfc85be68f949
Reviewed-on: https://gerrit.libreoffice.org/26877Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>