[5.1.x] Fixed #35643 -- Fixed a crash when ordering a QuerySet by a reference containing "__".

Regression in b0ad41198b.

Refs #34013. The initial logic did not consider that annotation aliases
can include lookup or transform separators.

Thanks Gert Van Gool for the report and Mariusz Felisiak for the review.
Backport of a16f13a866 from main.

django/db/models/sql/compiler.py

@@ -388,8 +388,13 @@ class SQLCompiler:
                 )
                 continue
 
-            ref, *transforms = col.split(LOOKUP_SEP)
-            if expr := self.query.annotations.get(ref):
+            if expr := self.query.annotations.get(col):
+                ref = col
+                transforms = []
+            else:
+                ref, *transforms = col.split(LOOKUP_SEP)
+                expr = self.query.annotations.get(ref)
+            if expr:
                 if self.query.combinator and self.select:
                     if transforms:
                         raise NotImplementedError(

tests/aggregation/tests.py

@@ -1750,6 +1750,26 @@ class AggregateTestCase(TestCase):
             ],
         )
 
+    def test_order_by_aggregate_default_alias(self):
+        publisher_books = (
+            Publisher.objects.values("book")
+            .annotate(Count("book"))
+            .order_by("book__count", "book__id")
+            .values_list("book", flat=True)
+        )
+        self.assertQuerySetEqual(
+            publisher_books,
+            [
+                None,
+                self.b1.id,
+                self.b2.id,
+                self.b3.id,
+                self.b4.id,
+                self.b5.id,
+                self.b6.id,
+            ],
+        )
+
     def test_empty_result_optimization(self):
         with self.assertNumQueries(0):
             self.assertEqual(