Don't add the frame to the toplevel stack if it hasn't been created yet.
In the event that a window is unreparented or destroyed, we usually need to add its frame window to the toplevel window stack until the time at which we recieve a DestroyNotify for it, as there may be incoming ConfigureNotify events puporting to stack other windows relative to that frame.
However, this does not apply in the case where we have not yet received a CreateNotify for the frame window. In that case, it is not possible for any stacking requests to be made relative to this window, so it does not need to be added immediately. Instead, we can add it at the time that we recieve a CreateNotify for it as a regular override redirect window until the time that it is later destroyed.