Add a diagnostic message rather than segfaulting on a closure having a missing outer context pointer.
Add a diagnostic message rather than segfaulting on a closure having a missing outer context pointer.

cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp