has_engine() ignores provided dataset if default dataset is set

[vinceatbluelabs]

How to reproduce:

Initialize an engine with a default dataset (e.g., engine = create_engine('bigquery:///test_pybigquery'))

Create a table named 'mytable' in a dataset named 'other_schma'

Call engine.has_table() with an explicit dataset provided (engine.has_table(table_name='mytable', schema='other_schema'))

Expected result

True

Observed result

False

Notes

The logic in question is here: https://github.com/mxmzdlv/pybigquery/blob/master/pybigquery/sqlalchemy_bigquery.py#L371-L375

My read of the README here is that the dataset provided to create_engine() is a default dataset - and that the meaning of 'default' is one which is used when no dataset is provided.

If you agree that this is a legit issue, I can prep a PR if need be with updated tests.

[alonme]

This does seem like a legit issue to me, i agree.