Just so you know Assassin it doesn't matter if there where any when you where there as a witch spawn is rare (unless you remove most of the spawning spaces in 128 block area, how you start a witch farm), anyways if you do find one if you find it after 1.7 comes out if the hut was not loaded in 1.6.4 the game will not see the hut as a place witches can spawn.
"When killed, witches can drop a great number of items, including Glass Bottles, Glowstone Dust, Gunpowder, Redstone, Spider Eyes, Sticks, and Sugar. They drop 1–3 item types, each 0–2 times. The same type can be chosen multiple times, therefore it is possible to get up to six of one item, or up to two of 3 different items.
Witches also rarely drop Potions of Healing, Fire Resistance, Swiftness and Waterbreathing, but only when they are killed while drinking that potion."
Check the loaded area. It may have changed, but a while ago I tryed to build a witch farm and it failed, a big reason for this was on the lolnet survival server only 3 chunks were loaded around a player (the chunk you are in plus 1 each side) so farms like witch and iron trench would not work.
This may have changed tho. Please check as I am keen to come back on and do some of these builds if this has been expanded.