bpo-36412: fix a possible crash in dictobject.c's new_dict() (GH-12519)

Misc/NEWS.d/next/Core and Builtins/2019-03-23-19-51-09.bpo-36412.C7acGn.rst

+Fix a possible crash when creating a new dictionary.

Objects/dictobject.c

@@ -604,7 +604,9 @@ new_dict(PyDictKeysObject *keys, PyObject **values)
         mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
         if (mp == NULL) {
             dictkeys_decref(keys);
-            free_values(values);
+            if (values != empty_values) {
+                free_values(values);
+            }
             return NULL;
         }
     }