When a file URL is passed to WebEnginePage::acceptNavigationRequest,
don't allow QtWebEngine to decide what to do with it (open it in the
QWebEnginePage or not) but let Konqueror make the choice according to
the user's configuration.
Whitout this change, clicking on the "Home" link in the introduction
page (konq:konqueror) opens the page in WebEnginePart, while it should
open it in DolphinPart (or whichever part the user has chosen to display
directories).