Allow system images larger than 2GiB, pt. 2

We need to patch zipfile during close() too, because it refers to the
ZIP64 file size threshold when writing out the central directory

Bug: 18015246
Bug: 19888174

Change-Id: I1b49d653d0831fcc2106808f86c929d7a2b22ff3
Signed-off-by: Greg Hackmann <ghackmann@google.com>