Don't set gi_frame to Py_None, use NULL instead, eliminating some insane

pointer dereferences.

Include/genobject.h

@@ -13,6 +13,7 @@ typedef struct {
 	PyObject_HEAD
 	/* The gi_ prefix is intended to remind of generator-iterator. */
 
+	/* Note: gi_frame can be NULL if the generator is "finished" */
 	struct _frame *gi_frame;
 
 	/* True if generator is being executed. */