Otherwise, we might process a lookup thousands of times, with no
benefit.  This pathological case was hit by Noto Nastaliq Urdu Draft
in Firefox's code to determine whether space glyph is involved in
any GSUB/GPOS rules.  A test page is at http://behdad.org/urdu

See:
https://bugzilla.mozilla.org/show_bug.cgi?id=1090869

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=84491

Fixes https://github.com/behdad/harfbuzz/pull/51

Useful for code-coverage generation of the ragel-generated files
as they will now contain the correct .hh filename in them.

When compiling with -O0, zero-sized constructors were showing up
and confusing the test.

Fine!

https://code.google.com/p/chromium/issues/detail?id=406957

By defining HB_NO_WIN1256.