started life as sal_uIntPtr and the various checks are typically
nPos < thing.size() just checking one bound, so sal_uInt32 looks safer
after all

Change-Id: Ibac839fc45b10d96ce4d4c8002fd26b20f70ae1c
Reviewed-on: https://gerrit.libreoffice.org/46697Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>