Closes #15396: memory leak in tkinter

Doc/ACKS.txt

@@ -120,6 +120,7 @@ docs@python.org), and we'll be glad to correct the problem.
    * Thomas Lamb
    * Detlef Lannert
    * Piers Lauder
+   * Julia Lawall
    * Glyph Lefkowitz
    * Robert Lehmann
    * Marc-André Lemburg

Modules/_tkinter.c

@@ -3135,8 +3135,10 @@ PyInit__tkinter(void)
 
     PyDict_SetItemString(d, "TkappType", (PyObject *)&Tkapp_Type);
 
-    if (PyType_Ready(&Tktt_Type) < 0)
+    if (PyType_Ready(&Tktt_Type) < 0) {
+        Py_DECREF(m);
         return NULL;
+    }
     PyDict_SetItemString(d, "TkttType", (PyObject *)&Tktt_Type);
 
     Py_TYPE(&PyTclObject_Type) = &PyType_Type;