Refactoring codes that cast XFastAttributeList reference
to FastAttributeList pointer using the helper function.

Change-Id: Iecf4b815d6556b0992d638b633260fbd459c0dc4
Reviewed-on: https://gerrit.libreoffice.org/39723Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>