REGRESSION (r132699): Crashes in WebCore::TextIterator::handleTextNodeFirstLetter
https://bugs.webkit.org/show_bug.cgi?id=100688

Reviewed by Martin Robinson.

Prevent crashes when accessibilityObjectIsIgnored calls textUnderElement
while a subtree is being destroyed.

Covered by existing tests.

* accessibility/atk/AccessibilityObjectAtk.cpp:
(WebCore::AccessibilityObject::accessibilityPlatformIncludesObject):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140166 268f45cc-cd09-0410-ab3c-d52691b4dbfc