Blank Issues should be enabled if they are not explicit disabled through
the `blank_issues_enabled` field of the Issue Config. The Implementation
has currently a Bug: If you create a Issue Config file with only
`contact_links` and without a `blank_issues_enabled` field,
`blank_issues_enabled` is set to false by default.
The fix is only one line, but I decided to also improve the tests to
make sure there are no other problems with the Implementation.
This is a bugfix, so it should be backported to 1.20.
1c039b4e1e