Rendermode 3D preview is being rendered continously even if nothing changes in the scene

This happens because EffectReference dirty flag is always set when Qt5RenderNodeInstanceServer::collectItemChangesAndSendChangeCommands() is called and root node is a 3D item. It also seems to be the only flag ever to be set on content item of the root instance even if there are changes to the scene, so checking the dirty flags of root instance content item there seems to be useless.