Fixing missing characters (only characters of the basic Control font
showed by Insert special character dialog) and freezing (when
LibreOffice tried to replace hundred of characters [missing from the
chosen font] during scrolling in the insert special character dialog).

Change-Id: I8fd5bd233f16572eb2b740a8f8e7e8608c19d06f
Reviewed-on: https://gerrit.libreoffice.org/17792Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>