Handle PyString_FromInternedString() failing (unlikely, but possible).
Handle PyString_FromInternedString() failing (unlikely, but possible).

Klocwork #325

(I'm not backporting this, but if someone wants to, feel free.)

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator