Changed the solution https://gerrit.libreoffice.org/#/c/70786/
of Vasily sligthly, so MS Office can recognize fields still
as fields.

Change-Id: Id45330a96dfe002685c6ef3dc62e408c5f9f46c4
Reviewed-on: https://gerrit.libreoffice.org/72868
Tested-by: Jenkins
Reviewed-by: Vasily Melenchuk <vasily.melenchuk@cib.de>