Bounds check in CFX_Font::LoadGlyphPath().

Add a check to CFX_Font::LoadGlyphPath() similar to the one that exists
in CFX_FaceCache::RenderGlyph().

Also replace some scattered magic numbers in the file with constants,
and make arrays not used outside this file be statically scoped.

BUG=406144
R=jun_fang@foxitsoftware.com

Review URL: https://codereview.chromium.org/497863002