AAT::Lookup has no other way to detect whether it is returned from
a real and sanitized font data or from a null pool, this checks if
the table has been recognized valid by sanitizer by checking
table's major version which is zero if returned from a null pool and
non-zero if is from a sanitized font data, it is expected the other
calls of the table (unlikely to have more calls however) also do a
similar version check before calling the lookups used on the table.
They aren't contributing to rendering and making issue for stroking, let's skip them
ourselves as Skia does also https://skia-review.googlesource.com/c/skia/+/268166
They are useful for extracting extents and so which that functionality won't be effected by this change.
Specially checks correctness of the API semantics:
* no move happens when a path is already opened with move-to.
* no path will be left open and close-path will happen at the end of opened paths.
* no path opens with a move-to and will be closed with no length.
* paths start and ending points matches.
* no line/quadratic/cubic command will be issued when no path is started.
Khaled Hosny
Ebrahim Byagowi