[oo] Fixed a semi-predicate problem in Parrot_oo_find_vtable_override_for_class(), where the function ignored the cached absence of a VTABLE override.  Respecting the case where Parrot's already performed the lookup and found no override improves the Rakudo-building benchmark by 10.42%.  The improvement is similar in other heavily OO code.
[oo] Fixed a semi-predicate problem in
Parrot_oo_find_vtable_override_for_class(), where the function ignored the
cached absence of a VTABLE override.  Respecting the case where Parrot's
already performed the lookup and found no override improves the Rakudo-building
benchmark by 10.42%.  The improvement is similar in other heavily OO code.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@38847 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot