Prevent crash on shutdown which can occur if we are finalizing

and the module dict has been cleared already and some object
raises a warning (like in a __del__).

Will backport.

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.6 alpha 1?
 Core and builtins
 -----------------
 
+- Prevent seg fault on shutdown which could occur if an object
+  raised a warning.
+
 - Bug #1566280: Explicitly invoke threading._shutdown from Py_Main,
   to avoid relying on atexit.
 

Python/errors.c

@@ -640,7 +640,8 @@ PyErr_WarnEx(PyObject *category, const char *message, Py_ssize_t stack_level)
 
 	if (warnings_module != NULL) {
 		dict = PyModule_GetDict(warnings_module);
-		func = PyDict_GetItemString(dict, "warn");
+		if (dict != NULL)
+			func = PyDict_GetItemString(dict, "warn");
 	}
 	if (func == NULL) {
 		PySys_WriteStderr("warning: %s\n", message);