Correct glyph with non-bmp from typeface on Mac.

CTFontGetGlyphsForChars puts the glyph id at the index of the lead
surrogate as is documented in comments, but the code is looking at
the index of the trail surrogate.

BUG=skia:2960
R=mtklein@google.com

Author: bungeman@google.com

Review URL: https://codereview.chromium.org/596413002
2 files changed