getParent()->moveChildToFront() causes exception sometimes

[LRitesh]

If I listen to mouse events on a child node and try to move it to front on mouse click with something like-
getParent()->moveChildToFront((NodeRef) (this))
it causes an exception inside Signals.h.

This is probably not the best way to do this anyway. Changing it so that the parent node can observe mouse events on child node, and calling moveChildToFront there doesn't cause this. But opening an issue so we can look into this later.