It fixes#7625.
If the Top DICT's Private DICT extends past the end of the font data,
the Local Subrs INDEX is unreachable and every CharString that calls
a subr ends up as a blank glyph. Throw from parsePrivateDict so the
existing catch in translateFont triggers fallbackToSystemFont, then
run getFontSubstitution post-construction so we pick a close local
match instead of the generic fallbackName.
