Fix crash when the stackref is NULL.

Author: ZeroIntensity

Python/bytecodes.c

@@ -4304,6 +4304,7 @@ dummy_func(
             EXIT_IF(meth->ml_flags != (METH_FASTCALL|METH_KEYWORDS));
             PyTypeObject *d_type = method->d_common.d_type;
             PyObject *self = PyStackRef_AsPyObjectBorrow(arguments[0]);
+            EXIT_IF(self == NULL);
             EXIT_IF(!Py_IS_TYPE(self, d_type));
             STAT_INC(CALL, hit);
             int nargs = total_args - 1;
@@ -4382,6 +4383,7 @@ dummy_func(
             PyMethodDef *meth = method->d_method;
             EXIT_IF(meth->ml_flags != METH_FASTCALL);
             PyObject *self = PyStackRef_AsPyObjectBorrow(arguments[0]);
+            EXIT_IF(self == NULL);
             EXIT_IF(!Py_IS_TYPE(self, method->d_common.d_type));
             STAT_INC(CALL, hit);
             int nargs = total_args - 1;