Page Comparison

IN:
     IX = filter handle

OUT, if call successful:
     Fc = 0
     A = character from filter
     Fz = 1, if character is converted, else 0

OUT, if call failed:
     Fc = 1
     A = error code:
          RC_HAND ($08), Bad filter handle
          RC_EOF ($09), Filter is empty

Registers changed after return:
     ..BCDEHL/IXIY same
     AF....../.... different