convert sal_Char* to OUString

I can see no reason to store sBulletName as an sal_Char* instead
of converting backwards and forwards from OUString

Change-Id: Ib16b9f04c5738aa2346c9b5b4f28461fc8b60c4f
Reviewed-on: https://gerrit.libreoffice.org/8641
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>