AttributeError: 'NoneType' object has no attribute 'normalized'

ERROR:
```
from sql_metadata import Parser
rawSQL1 = '''
with aa as --sdfsdfsdf
(SELECT * from table1)
SELECT * FROM aa
'''
tbls = Parser(rawSQL1).tables
```

NO ERROR:
```
from sql_metadata import Parser
rawSQL1 = '''
with aa --sdfsdfsdf
as
(SELECT * from table1)
SELECT * FROM aa
'''
tbls = Parser(rawSQL1).tables
```

Crashes if exist comment sign '--' after 'AS'