[qt5web] initialize QWebEngine only when create QApplication
[qt5web] initialize QWebEngine only when create QApplication

If application already exists, operation is not legal
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olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root