Nonsense. Supply and demand are not perfectly elastic. Consider a simplified hypothetical world where Alice harvests carrots that magically fall from heaven, Alice and Bob need 10 carrots per day to survive, and a total of 15 carrots fall from heaven every day. There is no other source of food. Alice eats ten carrots, and sells five to Bob. Bob's carrot-demand is at least ten carrots, but he can't buy them at any price, no matter how desperately he may need them to keep starvation at bay.
Yes, there is such a thing as a shortage.