Fraction: rewrite condition 'GetDenominator()==-1'
Fraction: rewrite condition 'GetDenominator()==-1'

Change-Id: I483024fd0ef3e4e187a143631b2e8bd953fa3a52
Reviewed-on: https://gerrit.libreoffice.org/12240
Reviewed-by: Julien Nabet <8a36cd9f353d245c534f8bb105741cdef632bfd5@yahoo.fr>
Reviewed-by: David Tardon <120ec0d1a1a64b2795847ed1f99512646e9f2768@redhat.com>
Tested-by: David Tardon <120ec0d1a1a64b2795847ed1f99512646e9f2768@redhat.com>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core