Wait for Quality Gate fails for projects that do not yet have a new code period

Scanning the default branch of a project with the `sonar.qualitygate.wait` property enabled fails when there is no new code period set (because there is no quality gate available for the default branch).

This is confusing for users because when they create a new project and launch a scan of the default branch their scan command will fail with the following message:

"QUALITY GATE STATUS: FAILED"

In reality the quality gate did not fail, there was just no QG computed because no new code period was set.