[autopr] Ignore repositories without default branch

[nemanja-boric-sociomantic]

Neptune currently fails with an exception if it finds the repository without a default branch. Instead, the repository should just be ignored.

[mathias-baumann-sociomantic]

Is that the current problem why it isn't running?

[mathias-baumann-sociomantic]

I am pretty sure this is not the problem. The exception is not from what you said. It's merely logging a problem but not stopping because of that.