HNSW: Fix leak of linklists in the index destructor.
HNSW: Fix leak of linklists in the index destructor.

ElList_ is not a part of the optimized index, so it's empty in indexes loaded from files.
In this case, its size cannot be used to determine number of elements.
data_rearranged_, which is always present in optimized indexes, may be used instead.

nmslib/nmslib,nmslib/nmslib,nmslib/nmslib,nmslib/nmslib,nmslib/nmslib,nmslib/nmslib,nmslib/nmslib