PythonCalcSplitConditionRule is not working as expected

Currently if users write such a SQL:

`SELECT pyFunc5(f0, f1) FROM (SELECT e.f0, e.f1 FROM (SELECT pyFunc5(a) as e FROM MyTable) where e.f0 is NULL)`

It will be optimized to:

`FlinkLogicalCalc(select=[pyFunc5(pyFunc5(a)) AS f0])
+- FlinkLogicalCalc(select=[a], where=[IS NULL(pyFunc5(a).f0)])
+- FlinkLogicalLegacyTableSourceScan(table=[[default_catalog, default_database, MyTable, source: [TestTableSource(a, b, c, d)]]], fields=[a, b, c, d])`

The optimized plan is not runnable, we need to fix this.