Fix unicode_aswidechar() for 4b unicode and 2b wchar_t (AIX).

Misc/NEWS

@@ -7,6 +7,12 @@ What's New in Python 3.2.6?
 
 *Release date: TBD*
 
+Core and Builtins
+-----------------
+
+- Issue #19529: Fix a potential crash in converting Unicode objects to wchar_t
+  when Py_UNICODE is 4 bytes but wchar_t is 2 bytes, for example on AIX.
+
 Library
 -------
 

Objects/unicodeobject.c

@@ -1267,7 +1267,7 @@ unicode_aswidechar(PyUnicodeObject *unicode,
     Py_ssize_t nchar;
 
     u = PyUnicode_AS_UNICODE(unicode);
-    uend = u + PyUnicode_GET_SIZE(u);
+    uend = u + PyUnicode_GET_SIZE(unicode);
     if (w != NULL) {
         worig = w;
         wend = w + size;