[3.12] gh-128198: Add missing error checks for usages of PyIter_Next() (GH-128199) (GH-128273)

(cherry picked from commit 5c814c8)

Co-authored-by: Yan Yanchii <[email protected]>

Author: serhiy-storchaka

Objects/namespaceobject.c

@@ -121,6 +121,10 @@ namespace_repr(PyObject *ns)
             goto error;
     }
 
+    if (PyErr_Occurred()) {
+        goto error;
+    }
+
     separator = PyUnicode_FromString(", ");
     if (separator == NULL)
         goto error;