[3.12] gh-116448: Handle errors correctly in os_waitid_impl in posixmodule (GH-116449) (#116451)

gh-116448: Handle errors correctly in `os_waitid_impl` in `posixmodule` (GH-116449)
(cherry picked from commit 882fced)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

Author: miss-islington

Modules/posixmodule.c

@@ -9400,15 +9400,25 @@ os_waitid_impl(PyObject *module, idtype_t idtype, id_t id, int options)
     if (!result)
         return NULL;
 
-    PyStructSequence_SET_ITEM(result, 0, PyLong_FromPid(si.si_pid));
-    PyStructSequence_SET_ITEM(result, 1, _PyLong_FromUid(si.si_uid));
-    PyStructSequence_SET_ITEM(result, 2, PyLong_FromLong((long)(si.si_signo)));
-    PyStructSequence_SET_ITEM(result, 3, PyLong_FromLong((long)(si.si_status)));
-    PyStructSequence_SET_ITEM(result, 4, PyLong_FromLong((long)(si.si_code)));
-    if (PyErr_Occurred()) {
-        Py_DECREF(result);
-        return NULL;
-    }
+    int pos = 0;
+
+#define SET_RESULT(CALL)                                     \
+    do {                                                     \
+        PyObject *item = (CALL);                             \
+        if (item == NULL) {                                  \
+            Py_DECREF(result);                               \
+            return NULL;                                     \
+        }                                                    \
+        PyStructSequence_SET_ITEM(result, pos++, item);      \
+    } while(0)
+
+    SET_RESULT(PyLong_FromPid(si.si_pid));
+    SET_RESULT(_PyLong_FromUid(si.si_uid));
+    SET_RESULT(PyLong_FromLong((long)(si.si_signo)));
+    SET_RESULT(PyLong_FromLong((long)(si.si_status)));
+    SET_RESULT(PyLong_FromLong((long)(si.si_code)));
+
+#undef SET_RESULT
 
     return result;
 }