Fix versioning behavior with DAM

Requirements:

• Build: nuxeo-server-9.1-I20170406_0420-tomcat
• DAM
• Web UI

Steps to reproduce:

• jdoe add a Picture => no version, the button "create a version" is available
• jsmith edit the metadata => the version is now 0.2+ instead of 0.1+
• jdoe edit the metadata => version is now 0.4+ instead of 0.2+