Fix two CloneNonCycle issues

CloneNonCycle() tries to detect cyclic object references without copying
them. There are two issues:
-- for elements in an array or a dictionary, they should be able to
refer to the same object, which are not cyclic;
-- for cyclic referenced elements in an array or a dictionary, do not
clone the element at all. Having nullptr or <key, nullptr> as an element,
like we did before, might cause crash when the element being accessed.

BUG=chromium:701860

Change-Id: Id0304accde76ed06fa5ce640994c7628359600fb
Reviewed-on: https://pdfium-review.googlesource.com/3156
Commit-Queue: dsinclair <dsinclair@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>

0 files changed, 0 insertions, 0 deletions