The rewrite using CBOR internals replaced one of the two naked pointers
that were members of QJsonArray and QJsonObject with a
QExplicitlySharedDataPointer. The problem is that its operator= will
read the current value to decrement the refcount and possibly delete the
pointed object.
But QJson{Array,Object}::initialize() are called from inlined code,
without initialization. So we can't call operator=. We need to memcpy to
write a nullptr.
This is not unit-testable because it requires compiling against 5.14 or
earlier, then running against 5.15.
Fixes: QTBUG-82700
Change-Id: Iaa63461109844e978376fffd15f98c62656d197c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
30a0787907