fix save several file on by reseting the xstorable on close
fix save several file on by reseting the xstorable on close

Change-Id: I329d43e06b0c81cebda0464ebb0fff41714020a3
Reviewed-on: https://gerrit.libreoffice.org/6355
Reviewed-by: Tor Lillqvist <a9ff1a38c0d094d92725714af3aa7948469a0905@collabora.com>
Tested-by: Tor Lillqvist <a9ff1a38c0d094d92725714af3aa7948469a0905@collabora.com>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core