I wouldn't use it, and I engage in high risk brewing activities pretty regularly. The problem is that when you transferred beer out of the carboy, you pulled in whatever air was in the room in which you racked it. Air is full of mold spores, acetobacter, and all kinds of other things that love beer and oxygen together. If you purged with CO2 it would probably be ok, but the funk has had a couple weeks to grow in there, and the oxygen is all it needs to get going. Then you add your fresh wort, and there's no guarantee that you don't have a viable population of some other microbe. Plus a fresh pack of 05 is like 5 bucks. Practice safe brewing in this case, and don't risk an infection!