Reuse QVariantList memory on the deserialization side too.

In my opinion this should go upstream for all QDataStream
deserialization to avoid deallocation and reallocation of
memory if it is not necessary.

Change-Id: I17df81a79e834c39aabe09cee975d23000243b1b
Reviewed-by: Brett Stottlemyer <bstottle@ford.com>