a failed position returns false, but stays at the failed position, so
next time its called without moving it then it returns true

store what we return for a given position for reuse if the position
doesn't change

Change-Id: I404c65ac89eb6f5c867f62a62028b87effdbcbf8
Reviewed-on: https://gerrit.libreoffice.org/49308Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>