Depends how you define "bastard". The dictionary definition is "A child born outside wedlock", or "A child born to two people who aren't married to each other". The marital status of the parents doesn't really matter, just that they aren't married to each other. They could both be single, or both be married to someone other than each other, etc.

So now you have the question of whether Mary was married to whoever/whatever fathered Jesus, i.e. was Mary married to God? The question almost makes no sense, since God can only be said to be the father of Jesus using a very non-standard definition of "father". I'd hesitate to use the word "bastard" to refer to Jesus. I'd say that Jesus had no real "father".