GTK3 emits way too many style-updated, which triggers font cache updates. The
avoidance of unecessary font cache updates was first implemented in 29c55564.
Unfortuantely, it seems that the current font-options was never set as
last-seen font-options, so still to many fonts-changed were emitted

Change-Id: I01a47d4d7fb033e335b1a49ffa6e1bb98f7fd28d
Reviewed-on: https://gerrit.libreoffice.org/55287Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>