Fix downloads

[cormachallinanderilinx]

Fix for

• https://github.com/IATI/ckanext-iati/issues/430
• https://github.com/IATI/ckanext-iati/issues/426
• https://github.com/IATI/ckanext-iati/issues/424

Tested on:

• https://staging.iatiregistry.org/publisher/download/csv
• https://staging.iatiregistry.org/csv/download/abaseen
• https://staging.iatiregistry.org/publisher/download/json
• https://staging.iatiregistry.org/dashboard/recent-publishers/download

Also added: https://github.com/IATI/ckanext-iati/issues/427 Test: https://staging.iatiregistry.org/organization/asdb?country=Azerbaijan