Oj: Use-After-Free in Oj::Doc Iterators via Reentrant Close

Summary Oj::Doc iterators eachvalue, eachchild, eachleaf are vulnerable to a heap use-after-free. When a Ruby block yielded during iteration calls doc.close or d.close, the document's heap memory is freed while the C iterator is still running. When control returns from the block, the iterator rea...