Can't download integrity reports for large collection

The download integrity reports button on the Integrity page on the Web GUI fails when trying to download large files. 
This can be reproduced by trying to download the integrity reports from http://avis.bitmag-prod01.statsbiblioteket.dk/avis-webclient/.

Probably it tries to load the entire file into memory to zip it. Need a better login to zip a stream of data instead, so we don't need to load the entire file into memory.