...like UnsizedArrayOf<>.

This fixes a class of crasher bugs, mostly with color and AAT tables.  We
cannot use nullable offsets to varsized data that does not declare min_size,
because it's nost safe to use our fixed-size null pool for types that have
their size external.  So, use non_null'able offsets for these.

A further enhancement would be to make use of min_size in Null<> itself.
Will try that after.

Not sure how I didn't add before...

Fix a bug in CBDT sanitize, and redundant check in avar.

Sorry for the noise, downstream custom builders.  Please adjust.

We should hang those off somewhere else. For now, the unused ones can go.

I believe I'm happy with it now.

At any position, if state is not zero, mark unsafe-to-break before,
unless we can reason it safe.

At any position, if there's an action entry for end-of-text, mark
unsafe to break.

Also changes buffer diff impl to allow for flag differences as long
as the buffer glyph flags are superset of reference glyph flags.

With this, all MORX tests pass.

Remove the faulty loop-detection logic. Use max-ops for breaking
out of infinite loops or heavy work.

https://twitter.com/behdadesfahbod/status/958065026262183936

We form the Zapfino ligature now. Yay! No further testing done.

For run-time checking.

I hate it that with my compiler at least, it doesn't catch totally uncompilable
statements in templates if they are not used...

Maybe I should disable C++11 detection such that my compiler also catches
these.  Doesn't look like we can switch to it for a while anyway...

It's dead, Jim!

From old 'mort' table.

Such a headache that Windows defines UINT8, ...; Just prefix it.

c:\projects\harfbuzz\src\hb-aat-layout-common-private.hh(51): error C2872: 'UINT16': ambiguous symbol [C:\projects\harfbuzz\build\harfbuzz.vcxproj]
C:\Program Files (x86)\Windows Kits\10\Include\10.0.14393.0\shared\basetsd.h(80): note: could be 'unsigned short UINT16'
c:\projects\harfbuzz\src\hb-open-type-private.hh(648): note: or       'OT::UINT16'