Differential proteomics zipped download functionality is broken

[pcm32]

Calls to download the experiment as a zip file from the web application like this:

curl -v -o test.zip 'https://www.ebi.ac.uk/gxa/experiments/download/zip?&accession=E-PROT-39'

fail for proteomics differential studies in general. We suspect it is trying to add a specific file to the zip bundle, possibly a file existing in baseline proteomics but not differential. Given that proteomics experiments have some optional files in general, it might be worth changing the strategy of the part that generates the zip bundle to not fail when some files are not present.