Not going to lecture, I promise. I am an ex smoker myself.
1. The idea of fasting is to detoxify your body, to become more healthy. So obviously that would negate that whole point.
2. You will get very light headed and nautious from smoking while fasting. Possibly worse.
Think of it this way: There is going to be nothing coming into your body except for nicotine, which means that it will have that much more affect on you.
Have you ever drank on an empty stomach? It is like that times 100.
So just please think it over before doing something like that. One or the other, not both at the same time.