Avoid using 0 as the default winId in QPlatformWindow.

Avoid using 0 as the default winId in QPlatformWindow.

When the platform plugin does not reimplement QPlatformWindow::winId()
to return a non-zero value, the default implementation provides a WId
of 0. This breaks various scenarios with QWidgets which, for example
in nativeParentWidget(), rely on internalWinId() being non-zero for
TLWs.

As a result, apps like collidingmice will crash with the 'minimal'
platform plugin when they try to do markDirtyOnScreen for the graphics
view's viewport widget because viewport()->nativeParentWidget()
unexpectedly returns null, even though it should return the
QGraphicsView.

The patch makes the default value WId(1) in order to to avoid this.

Change-Id: Iafef2e510e32b5610b8cef742313e9119ed64963
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>