Skip the data dictionary when one does not exist

[janette]

ref: 21364

QA Steps

• [ ] Put site in DD reference mode
• [ ] Create a dataset without a DD
• [ ] Go to the dataset page, create a filter, grab the query url
• [ ] Add download bits like the following

https://dkan.ddev.site/api/1/datastore/query/c59d6e04-0735-5a18-b07b-a41b27b0659b/0/download?limit=20&offset=0&conditions[0][property]=year&conditions[0][value]=2012&conditions[0][operator]==&format=csv

• [ ] Confirm you get a file with the results you expect
• [ ] Confirm no errors in the file