When a configuration is locked, still a (locked!) preview must be possible to create

There are customers who want to lock the core (master) and do everything via branches. In this case, the master is always locked. When a webmaster opens the master in CM, an attempt to create a preview will be done in case there is no preview yet. However, for locked hst configuration, at this moment, a preview creation is not allowed. However, via branch creation (downstream project) still a preview is created. This is inconsistent and confusing.

Better to allow webmasters to create a preview of a locked configuration