In the following tree, the code cleaning up after the inner container node set
a nil current construction node report, causing
CurrentTreeConstructionNodeReport to panic with "CurrentConstructionNodeReport
may only be called during construction of the spec tree" when called by the
transformer for the following It:

    var _ = Describe("outer", func() {
        Context("inner", func() {
            ...
        })
        It("works", func() { ... })
    })

The fix is to restore the old value instead of setting to nil.