Selection issue dev 5_0

The node was reset to null after double-click
Problem described by https://trac.openmicroscopy.org.uk/ome/ticket/11853

To test
 * Double-click on a project containing datasets.
 * The Browse button should be active.
 * Double-click again on the project 
 * The Browse button should be still active. (it was not before)

see gh-1962