glyph index ranges are defined to be closed intervals, so don't add 1 to last_glyph

See mozilla bug https://bugzilla.mozilla.org/show_bug.cgi?id=880690 for details, and for the corresponding fix in Gecko.
Merge pull request #1 from jfkthame/patch-1

glyph index ranges are defined to be closed intervals, so don't add 1 to last_glyph