Trying to publish a failed changeset again is noop

Created by: eseliger

• Sourcegraph version: master
• Platform information: macOS 10.15.4, Chrome 81

Steps to reproduce:

1. Have a draft campaign (publishing needs to fail to repro, try no privilege token or so)
2. Click publish on one single changeset
3. It should fail, check the error messages in the campaign status
4. Click publish on the changeset again
5. See the spinner indicate something would happen

Expected behavior:

6. It is tried again

Actual behavior:

7. It only spins, no actual retry attempt is made. This piece of code just returns when a job exists (even if failed) https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/enterprise/internal/campaigns/service.go#L428-431