QML engine creates user plugins in QML thread when built statically

There's a difference of behaviour between building statically and dynamically.

When building statically my plugins will be created in the QML thread instead of main thread, because of qqmlimport.cpp (QQmlImportsPrivate::populatePluginPairVector())

This later makes my application crash because the plugin creates a QQmlComponent which is in a different thread than the QQmlEngine.