QmlJSInspector: Fixed multi-selection bug

Nothing useful can be done with multi-selection at the moment, but this
bug was introduced in 8d060151 and is
better to fix straight away.

What happened was that when multiple items are selected in the observed
QML application, Qt Creator would pick the first and send that back as
the new selection. This made it impossible to select more than one item.

Task-number: QTCREATORBUG-3426
Change-Id: I68283480af5e0a21e32e51a49848ff9a809ed5ec
Reviewed-on: http://codereview.qt.nokia.com/151


Reviewed-by: Kai Koehne <kai.koehne@nokia.com>