fix for empty NOT IN () in WHERE clause

[mikemorreale]

The following code gives an error for trying to do an empty NOT IN (), which is invalid SQL.

var list = [];
User.find().where({id: {not: list}}).exec(function (err, users) {
});

I added a small fix to use WHERE TRUE instead when this occurs.

[mikermcneil]

@mikemorreale Thank you- we're working on setting up a basic test suite for this module-- would you be interested in getting involved?

[mikemorreale]

Sure, I'd be happy to help out.