PublishIssues method fails for analysis of master branch

[jizi]

Current behaviour
Webhooks are delivered for analyses, not only for analyses of pull requests. When webhook for analysis of master branch is delivered it fails with error

sonarqube-pr-issues/cmd/server/run.go

Line 168 in 04a741c

return errors.Wrap(err, fmt.Sprintf("failed to find PR for branch %s of the project %s", branch, project))

Expected behaviour
There is an info logged and nil returned.