[BLOCKER-4.7.1] Instantiating a QWebSettings twice asserts

Instantiating a QDeclarativeWebView twice asserts

fixed in f532679ca11914b453e22342f2ae5e9f790ce47a

In a debug build this will trigger an assert:

import QtWebKit 1.0

WebView {
width: 640
height: 480
WebView {
}
}

This bug is also critical for tooling (Bauhaus).