Fix forwarding of keyboard events to multiple target items

Fix regression when multiple items are set to Keys.forwardTo attached
property. QML items accept key events automatically and event should be
by default in accepted state when entering handler.

Task-number: QTBUG-39168
Change-Id: Ibf6c163c4059269996113634efa48ad2fe4d838d
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>