Fixed #33449 -- Fixed makemigrations crash on models without Meta.order_with_respect_to but with _order field.

Regression in aa4acc164d.

tests/migrations/test_state.py

@@ -959,6 +959,44 @@ class StateTests(SimpleTestCase):
             ["id", "author"],
         )
 
+    def test_modelstate_get_field_order_wrt(self):
+        new_apps = Apps()
+
+        class Author(models.Model):
+            name = models.TextField()
+
+            class Meta:
+                app_label = 'migrations'
+                apps = new_apps
+
+        class Book(models.Model):
+            author = models.ForeignKey(Author, models.CASCADE)
+
+            class Meta:
+                app_label = 'migrations'
+                apps = new_apps
+                order_with_respect_to = 'author'
+
+        model_state = ModelState.from_model(Book)
+        order_wrt_field = model_state.get_field('_order')
+        self.assertIsInstance(order_wrt_field, models.ForeignKey)
+        self.assertEqual(order_wrt_field.related_model, 'migrations.author')
+
+    def test_modelstate_get_field_no_order_wrt_order_field(self):
+        new_apps = Apps()
+
+        class HistoricalRecord(models.Model):
+            _order = models.PositiveSmallIntegerField()
+
+            class Meta:
+                app_label = 'migrations'
+                apps = new_apps
+
+        model_state = ModelState.from_model(HistoricalRecord)
+        order_field = model_state.get_field('_order')
+        self.assertIsNone(order_field.related_model)
+        self.assertIsInstance(order_field, models.PositiveSmallIntegerField)
+
     def test_manager_refer_correct_model_version(self):
         """
         #24147 - Managers refer to the correct version of a