Make TTC fonts work again

osl::File::getFileURLFromSystemPath() does not return a boolean. I
wonder how this worked before, if it worked at all.

Change-Id: Iadc0e06236f43c24cbcd42e4fd79ac9116a58c13
Reviewed-on: https://gerrit.libreoffice.org/6769
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>