Avoid crash in handleTouchEvent and remove superfluous mapping.

252d1b34b2 introduces a mapFromGlobal
call in QWindowSystemInterface::handleTouchEvent. This has two issues:
It ignores the fact that the tlw parameter can be null, resulting in
an instant crash with the touch support of some platforms, and the
mapping itself is unneccessary because
QGuiApplication::processTouchEvent() will perform the same, the
rect set via setRect() is basically ignored due to the touchPoint.d.rect
= ... just before sending the final event to the widget in qguiapplication.cpp.

Using setScreenRect instead of setRect is a valid fix from the
previous patch, but the parts for the mapping need to be removed.

Change-Id: I0bb40c7d647fb062106b151e5987f9970d6ab2c8
Reviewed-on: http://codereview.qt-project.org/5448
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Bjørn Erik Nilsen <bjorn.nilsen@nokia.com>

src/gui/kernel/qwindowsysteminterface_qpa.cpp

@@ -235,14 +235,8 @@ void QWindowSystemInterface::handleTouchEvent(QWindow *tlw, ulong timestamp, QEv
         p.setScreenPos(screenPos);
         p.setScreenRect(point->area);
 
-        // Map screen pos to local (QWindow) coordinates and preserve sub-pixel resolution.
-        const QPointF delta = screenPos - screenPos.toPoint();
-        const QPointF localPos = tlw->mapFromGlobal(screenPos.toPoint()) + delta;
-        p.setPos(localPos);
-
-        QRectF rect(0, 0, point->area.width(), point->area.height());
-        rect.moveCenter(localPos);
-        p.setRect(rect);
+        // The local pos and rect are not set, they will be calculated
+        // when the event gets processed by QGuiApplication.
 
         p.setNormalizedPos(point->normalPosition);