Deleting an incubated object after setInitialState() crashes

Incubating objects are often parented in setInitialState(), which
can lead to the incubating object being deleted after object creation,
but before completion.  When incubator.clear() is called after
this point, it would attempt to delete the already deleted
object. This change guards the incubation object in the incubator.

Change-Id: I9585e93027250b8b6b3f1777b10ee1008ae7b818
Reviewed-by: Glenn Watson <glenn.watson@nokia.com>