[sfnt] Prevent overrunning in `post' table parser. * src/sfnt/ttpost.c (load_post_names): Get the length of `post' table and pass the limit of `post' table to load_format_20() and load_format_25(). (load_format_20): Stop the parsing when we reached at the limit of `post' table. If more glyph names are required, they are filled by NULL names. See Savannah bug #31040.