#63 notification fails when no view is open

[Randolf Schultz]

The notification callbacks of various tool objects
like Revolve, Extrude, Sweep, and Skin fail, when
no view is open (because there is no OpenGL context and
OpenGL matrix stack operations produce wrong results).
This happens e.g. when scenes containing such tool
objects but no views are loaded. Until a view is open
while notification runs, the notification of those
objects fails.