fix possible setdefault refleak (closes #17328)

Misc/NEWS

@@ -12,6 +12,8 @@ What's New in Python 3.3.1?
 Core and Builtins
 -----------------
 
+- Issue #17328: Fix possible refleak in dict.setdefault.
+
 - Issue #17223: array module: Fix a crasher when converting an array containing
   invalid characters (outside range [U+0000; U+10ffff]) to Unicode:
   repr(array), str(array) and array.tounicode(). Patch written by Manuel Jacob.

Objects/dictobject.c

@@ -2230,14 +2230,14 @@ dict_setdefault(register PyDictObject *mp, PyObject *args)
         return NULL;
     val = *value_addr;
     if (val == NULL) {
-        Py_INCREF(failobj);
-        Py_INCREF(key);
         if (mp->ma_keys->dk_usable <= 0) {
             /* Need to resize. */
             if (insertion_resize(mp) < 0)
                 return NULL;
             ep = find_empty_slot(mp, key, hash, &value_addr);
         }
+        Py_INCREF(failobj);
+        Py_INCREF(key);
         MAINTAIN_TRACKING(mp, key, failobj);
         ep->me_key = key;
         ep->me_hash = hash;