Additional warnings when processing cmap tables

Small enhancements to the code:
* Removed unused code that clips unicode characters to the baseplane
* Add a SAL_WARNING if the maximum character is greater than the
  minimum character.

Change-Id: I783fba75435e7f98a65afab2e091b737efc9ddc6
Reviewed-on: https://gerrit.libreoffice.org/7404
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>