XFA: merge patch from issue 803103002

Before this fix, the root will be released when an indirect object has the
same object number with the root. However, the root object is loaded when
the trailer is parsed. It shall not be updated or replaced anymore.

BUG=425040
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/803103002
1 file changed