Fix core dump in repr() of instancemethod whose class==NULL.

Objects/classobject.c

@@ -2058,6 +2058,9 @@ instancemethod_repr(PyMethodObject *a)
 	}
 	else
 		sfuncname = PyString_AS_STRING(funcname);
+	if (klass == NULL)
+		klassname = NULL;
+	else {
 		klassname = PyObject_GetAttrString(klass, "__name__");
 		if (klassname == NULL)
 			PyErr_Clear();
@@ -2067,6 +2070,7 @@ instancemethod_repr(PyMethodObject *a)
 		}
 		else
 			sklassname = PyString_AS_STRING(klassname);
+	}
 	if (self == NULL)
 		sprintf(buffer, "<unbound method %.100s.%.100s>",
 			sklassname, sfuncname);