patch 8.0.1280: Python None cannot be converted to a Vim type

Problem:    Python None cannot be converted to a Vim type.
Solution:   Convert it to v:none. (Ken Takata)
diff --git a/src/if_py_both.h b/src/if_py_both.h
index e717646..1801967 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -5713,7 +5713,7 @@
     }
     else
     {
-	if (run_ret != Py_None && ConvertFromPyObject(run_ret, rettv) == -1)
+	if (ConvertFromPyObject(run_ret, rettv) == -1)
 	    EMSG(_("E859: Failed to convert returned python object to vim value"));
 	Py_DECREF(run_ret);
     }
@@ -6231,6 +6231,11 @@
 
 	Py_DECREF(num);
     }
+    else if (obj == Py_None)
+    {
+	tv->v_type = VAR_SPECIAL;
+	tv->vval.v_number = VVAL_NONE;
+    }
     else
     {
 	PyErr_FORMAT(PyExc_TypeError,