Do you eat any time 1.5 hours prior to your workout? If so, when you workout, do you shit your drawers? Because if you do, I want to see that workout.
If not, then you don't have to worry about your body being completely empty. Cardio is basically nothing more than the cool down period after a hard workout. There are two types of cardio, one for fat burning (low to moderate intensity) one for cardiovascular conditioning (high intensity). You want your glycogen stores to be depleted as possible for when you do fat burning cardio, otherwise before you can burn fat, you have to empty the g.s. first. By design, the product of the body is used for muscle exertion and contraction (while in the gym). So after burning as much as you can with weight training which stresses the muscles and causes contraction, you are placing your body in the best environment possible to burn fat.
If your protein levels are high enough, and they should be since you are attempting to keep the calories up with limited carbs so you lose fat, then you are safe to wait until the entire training session is over.
If you are not sure or you just want to make sure you cover your bases, then the best thing to do is after you finish the weight training, take in 6-8 grams of BCAAs, 5 grams L-Glutamin, and 5 grams L-Arginine. In water with no carbs or fats. You can get a custom blend designed for you at Custom Caps, or you can go to Beyond-A-Century.com and order the powder form like I do. Just avoid tabs and hard press pills because you want immediate absorbtion. This will give your body near instant nutrients that only need to be absorbed and not broken down and digested ( as the general definition of digestion goes) so you can still hit up the cardio with a decent effort and not have a heavy stomach like you would following a protein shake.