Fix package generation when reverting to an older release commit

In Nuxeo Studio

• In branch management screen, edit current version
• Choose a version number, e.g. 1.0.0
• You work now on a 1.0.0-SNAPSHOT version
• Make some commits
• Generate a release => Choose next version number, e.g. 2.0.0
• You now work on a 2.0.0-SNAPSHOT version
• Make some commits
• Revert to a commit that was made before the release of version 1.0.0
• Try to download the package

=> it fails, you see an error instead

• In the branch management screen, edit the next version number, e.g. 2.0.1
• You now work on a 2.0.1-SNAPSHOT version
• Try to download the package

=> It works fine

Reason is a build is not generated for a SNAPSHOT when reverting on an older commit