broken overrideCursor handling in drag&drop in QWS

In src/gui/kernel/qdnd_qws.cpp QApplication::changeOverrideCursor is sometimes called without a QApplication::setOverrideCursor. If the application sets its own overrideCursor the changeOverrideCursor will change the overrideCursor of the application.
As a result the cursor to get stuck at Qt::ForbiddenCursor.
I can trigger this by random selection and dragging on a QWebView.