Fixed a potential crash in QDockWidget
Fixed a potential crash in QDockWidget

This happened when inserting the gap over a place holder item.

Task-number: QTBUG-6107
Reviewed-by: Gabi

pruiz/wkhtmltopdf-qt,RLovelett/qt,KDE/qt,igor-sfdc/qt-wk,KDE/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,RLovelett/qt,KDE/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,RLovelett/qt,igor-sfdc/qt-wk,RLovelett/qt,RLovelett/qt,KDE/qt,KDE/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,KDE/qt,KDE/qt,RLovelett/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,RLovelett/qt,RLovelett/qt,RLovelett/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,KDE/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,RLovelett/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt