SA14/Tests: Do not pass params=None to crate_before_execute

Specifically, for the non-bulk case. In case of validating bulk updates,
it is still left to `None`.

Croaks otherwise::

      File "/Users/amo/dev/crate/sources/crate-python/src/crate/client/sqlalchemy/tests/compiler_test.py", line 58, in test_crate_update_rewritten
        assert hasattr(clauseelement, '_crate_specific') is True
    AssertionError

src/crate/client/sqlalchemy/tests/compiler_test.py

@@ -45,14 +45,14 @@ def setUp(self):
 
     def test_sqlite_update_not_rewritten(self):
         clauseelement, multiparams, params = crate_before_execute(
-            self.sqlite_engine, self.update, self.values, None
+            self.sqlite_engine, self.update, self.values, {}
         )
 
         assert hasattr(clauseelement, '_crate_specific') is False
 
     def test_crate_update_rewritten(self):
         clauseelement, multiparams, params = crate_before_execute(
-            self.crate_engine, self.update, self.values, None
+            self.crate_engine, self.update, self.values, {}
         )
 
         assert hasattr(clauseelement, '_crate_specific') is True