Add missing init of TIsAProxy::fNextLastSlot.
Add missing init of TIsAProxy::fNextLastSlot.

(thanks valgrind for pointing this out)

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root