Fix crash on close due to an uninitialized pointer in QEventDispatcherQPAPrivate.

ISSUE: 497 (http://code.google.com/p/phantomjs/issues/detail?id=497)

Author: milianw

src/qt/src/gui/kernel/qeventdispatcher_qpa.cpp

@@ -121,6 +121,7 @@ class QEventDispatcherQPAPrivate : public QEventDispatcherUNIXPrivate
            barrierBeforeBlocking(0),
            barrierReturnValue(0),
            selectReturnMutex(0),
+           selectWorker(0),
            selectWorkerNeedsSync(true),
            selectWorkerHasResult(false),
            m_integrationInitialised(false),