gh-159739: Handle OrderedDict item iterator allocation failures (#159774)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Author: jelle-openai

Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.5a6e94.rst

@@ -0,0 +1,2 @@
+Avoid a crash when memory allocation fails while creating a
+:class:`collections.OrderedDict` items iterator.

Objects/odictobject.c

@@ -1941,22 +1941,21 @@ odictiter_new(PyODictObject *od, int kind)
     odictiterobject *di;
     _ODictNode *node;
     int reversed = kind & _odict_ITER_REVERSED;
-
-    di = PyObject_GC_New(odictiterobject, &PyODictIter_Type);
-    if (di == NULL)
-        return NULL;
+    PyObject *result = NULL;
 
     if ((kind & _odict_ITER_ITEMS) == _odict_ITER_ITEMS) {
-        di->di_result = _PyTuple_FromPairSteal(Py_None, Py_None);
-        if (di->di_result == NULL) {
-            Py_DECREF(di);
+        result = _PyTuple_FromPairSteal(Py_None, Py_None);
+        if (result == NULL) {
             return NULL;
         }
     }
-    else {
-        di->di_result = NULL;
+    di = PyObject_GC_New(odictiterobject, &PyODictIter_Type);
+    if (di == NULL) {
+        Py_XDECREF(result);
+        return NULL;
     }
 
+    di->di_result = result;
     di->kind = kind;
     Py_BEGIN_CRITICAL_SECTION(od);
     node = reversed ? _odict_LAST(od) : _odict_FIRST(od);