Fix HHVM fatal error when presenting closures.
Fix HHVM fatal error when presenting closures.

See facebook/hhvm#3812
lvht/psysh,mubassirhayat/psysh,adetch/psysh,damiankloip/psysh,lvht/psysh,damiankloip/psysh,damiankloip/psysh,mubassirhayat/psysh,bobthecow/psysh,adetch/psysh,bobthecow/psysh