[bdf, pcf] Support ISO646.1991-IRV character encoding (aka ASCII).

Problem reported by Marek Kašík <mkasik@redhat.com>, cf.

  https://bugzilla.redhat.com/show_bug.cgi?id=1451795

* src/bdf/bdfdrivr.c (BDF_Face_Init), src/pcf/pcfdrivr.c
(PCF_Face_Init): Implement it.
3 files changed