Response status codes are not handled in the server, because the upload response is null

[provokateurin]

I noticed that the web frontend doesn't handle errors like 507, because in https://github.com/nextcloud/server/blob/a9635044e35dadc0065889f62801173ad190863f/apps/files/src/views/FilesList.vue#L719-L719 the upload.response is just null.

To reproduce, just set a quota for the account and then upload a new file that would make the total storage usage go over the allowed quota. I only tested this with chunked uploads, so it could be specific to that.