On eglfs doubleclicks are not delivered

The bugfix of QTBUG-36364 brakes the doubleclick delivery on eglfs platform, because of an issue in QGuiApplicationPrivate::processMouseEvent().
With eglfs platform plugin the MouseEvent passed to this function will always have QWindow set to NULL. This is spotted within
QGuiApplicationPrivate::processMouseEvent and the local window pointer is set to a valid window. At the end of the function when the double click is handled there is the following line:
if (!e->window.isNull()) { // QTBUG-36364, check if window closed in response to press

In the eglfs case this is always NULL and so no double click events are ever sent.

You can see the commit that broke this here:
https://codereview.qt-project.org/#/c/76748/

Possible fix is to place the change inside of a #ifndef Q_WS_QPA if it will not cause problems with future wayland support.