This simply shortcuts the glyph loading if FT_LOAD_ADVANCE_ONLY
is specified by FT_Get_Advances and the `hdmx` data are located.
Particularly, the classic v35 interpreter or "verified" ClearType
fonts might see 100x speed up in retrieving the hdmx cache.

* src/truetype/ttgload.c (TT_Load_Glyph): Insert the shortcut.