FolderChooserListViewBase#getAvailablePathsExpression is now null robust

FolderChooserListViewBase#getAvailablePathsExpression threw a TypeError because of an unallowed null access when no preferred site was selected. This occurred while importing an item from the content hub.

(CMS-19707)

Controlroom: Start translation workflow button in toolbar hidden when unusable

A bug has been fixed which shows the button to start a translation even if it is not possible to start a translation. Now the button is hidden in the case a translation can't be started.

(CMS-16881)