[4.2.x] Fixed #34486 -- Fixed DatabaseOperations.compose_sql() crash with no existing database connection on PostgreSQL.

Regression in 09ffc5c121.

Backport of 53aee470d5 from main

tests/backends/postgresql/tests.py

@@ -420,3 +420,13 @@ class Tests(TestCase):
         with self.assertRaisesMessage(NotSupportedError, msg):
             connection.check_database_version_supported()
         self.assertTrue(mocked_get_database_version.called)
+
+    def test_compose_sql_when_no_connection(self):
+        new_connection = connection.copy()
+        try:
+            self.assertEqual(
+                new_connection.ops.compose_sql("SELECT %s", ["test"]),
+                "SELECT 'test'",
+            )
+        finally:
+            new_connection.close()