Returning 404 while resource used in POST does not exist

[agatatalita]

A very low priority, just to keep in mind.
There may be a better status to return.

https://stackoverflow.com/questions/50643217/http-status-while-post-with-incorrect-data-using-id-of-resource-which-does-not

ditapi/test/user-tags.js

Line 326 in 70d2cc7

it('[nonexistent tagname] error 404', async function () {