Problem: Cannot preview or download files in the Appraisal tab from GPG encrypted space

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Expected behaviour

Files in backlog transfers can be previewed and downloaded from the Appraisal tab.

Current behaviour

If the backlog transfer is stored in a GPG encrypted space clicking on the Preview file pane or the Download link below results in an error like this:

Steps to reproduce

1. Create a GPG encryption on Local Filesystem space in the Storage Service.
2. Add a Transfer Backlog location to the GPG space. Ensure this new location is the only one enabled for this type.
3. Start a transfer and send it to the backlog.
4. Search the new transfer in Appraisal tab and try to preview or download any of its files from the Analysis pane.
5. You should see an error with {"success": false, "message": "Storage service returned 501; check logs?"} like above.

Your environment (version of Archivematica, operating system, other relevant details)

artefactual/archivematica@37ba46a

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For Artefactual use:

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