tdf#83889:FILEOPEN:PPTX bullet point is followed by spurious symbol

If we have first numeric bullet and then insert any symbol bullet on same level
then suffix of numeric bullet continues with symbol
bullet as well.
Solution : Reset suffix to none if it is symbol bullet.

Change-Id: I06dddec55c6f3d8cc1545d30f7228ca08cb81396
Reviewed-on: https://gerrit.libreoffice.org/14890
Tested-by: Jenkins <ci@libreoffice.org>
Tested-by: David Tardon <dtardon@redhat.com>
Reviewed-by: David Tardon <dtardon@redhat.com>