Fix range boundary when parsing encoding for CFF font with custom encoding 1

from CFF format specification, format 1 has the following makeup:
card8: first character in range
card8: number of additional characters (excluding the first)

This change corrects the calculation of the code of the last character in range
to respect the fact that the additional character specification excludes the
first character in the range.
Merge pull request #1487 from timheilig/bug_cff_enc_end_of_range

Fix range boundary parsing encoding for CFF font with custom encoding 1