Replace incorrect usage of GLYPH_ASCII_TABLE_SIZE with correct
KERNING_CACHE_TABLE_SIZE

I probably made this mistake years ago. We have one define - GLYPH_ASCII_TABLE_SIZE - which is used with our glyph cache, and another - KERNING_CACHE_TABLE_SIZE - which is used with our kerning cache. This patch corrects two instances of incorrect usage.

They both are the same value, 128, so this does not cause any real problems. However it is still an error. And I can can foresee proposed changes that would eliminate the glyph ascii table if we start hashing those by glyph index instead of by codepoint. I can also imagine changes to our kerning cache that could expand that to 65535.