Fix core dump in PyArg_ParseTuple() with Unicode arguments.

Reported by Fredrik Lundh on python-dev.

The conversimple() code that handles Unicode arguments and converts
them to the default encoding now calls converterr() with the original
Unicode argument instead of the NULL returned by the failed encoding
attempt.

Python/getargs.c

@@ -367,7 +367,8 @@ convertitem(PyObject *arg, char **p_format, va_list *p_va, int *levels,
 static char *
 converterr(char *expected, PyObject *arg, char *msgbuf)
 {
-	assert (expected != NULL);
+	assert(expected != NULL);
+	assert(arg != NULL); 
 	sprintf(msgbuf, "must be %.50s, not %.50s", expected,
 		arg == Py_None ? "None" : arg->ob_type->tp_name);
 	return msgbuf;
@@ -387,6 +388,7 @@ convertsimple(PyObject *arg, char **p_format, va_list *p_va, char *msgbuf)
 {
 	char *format = *p_format;
 	char c = *format++;
+	PyObject *uarg;
 	
 	switch (c) {
 	
@@ -568,12 +570,12 @@ convertsimple(PyObject *arg, char **p_format, va_list *p_va, char *msgbuf)
 			}
 #ifdef Py_USING_UNICODE
 			else if (PyUnicode_Check(arg)) {
-				arg = UNICODE_DEFAULT_ENCODING(arg);
-				if (arg == NULL)
+				uarg = UNICODE_DEFAULT_ENCODING(arg);
+				if (uarg == NULL)
 					return converterr(CONV_UNICODE,
 							  arg, msgbuf);
-				*p = PyString_AS_STRING(arg);
-				*q = PyString_GET_SIZE(arg);
+				*p = PyString_AS_STRING(uarg);
+				*q = PyString_GET_SIZE(uarg);
 			}
 #endif
 			else { /* any buffer-like object */
@@ -591,11 +593,11 @@ convertsimple(PyObject *arg, char **p_format, va_list *p_va, char *msgbuf)
 				*p = PyString_AS_STRING(arg);
 #ifdef Py_USING_UNICODE
 			else if (PyUnicode_Check(arg)) {
-				arg = UNICODE_DEFAULT_ENCODING(arg);
-				if (arg == NULL)
+				uarg = UNICODE_DEFAULT_ENCODING(arg);
+				if (uarg == NULL)
 					return converterr(CONV_UNICODE,
 							  arg, msgbuf);
-				*p = PyString_AS_STRING(arg);
+				*p = PyString_AS_STRING(uarg);
 			}
 #endif
 			else
@@ -622,12 +624,12 @@ convertsimple(PyObject *arg, char **p_format, va_list *p_va, char *msgbuf)
 			}
 #ifdef Py_USING_UNICODE
 			else if (PyUnicode_Check(arg)) {
-				arg = UNICODE_DEFAULT_ENCODING(arg);
-				if (arg == NULL)
+				uarg = UNICODE_DEFAULT_ENCODING(arg);
+				if (uarg == NULL)
 					return converterr(CONV_UNICODE,
 							  arg, msgbuf);
-				*p = PyString_AS_STRING(arg);
-				*q = PyString_GET_SIZE(arg);
+				*p = PyString_AS_STRING(uarg);
+				*q = PyString_GET_SIZE(uarg);
 			}
 #endif
 			else { /* any buffer-like object */
@@ -648,11 +650,11 @@ convertsimple(PyObject *arg, char **p_format, va_list *p_va, char *msgbuf)
 				*p = PyString_AsString(arg);
 #ifdef Py_USING_UNICODE
 			else if (PyUnicode_Check(arg)) {
-				arg = UNICODE_DEFAULT_ENCODING(arg);
-				if (arg == NULL)
+				uarg = UNICODE_DEFAULT_ENCODING(arg);
+				if (uarg == NULL)
 					return converterr(CONV_UNICODE,
 							  arg, msgbuf);
-				*p = PyString_AS_STRING(arg);
+				*p = PyString_AS_STRING(uarg);
 			}
 #endif
 			else