HyperLogLog sparse to dense conversion function.
Create HyperLogLog objects with sparse encoding.
Fix HLL sparse object creation.

The function didn't considered the fact that each XZERO opcode is
two bytes.
Increment pointer while iterating sparse HLL object.
Fix HLL sparse object creation #2.

Two vars initialized to wrong values in createHLLObject().
Macro HLL_SPARSE_XZERO_LEN fixed.
hllSparseSum(): multiply 1 * runlen for zero entries.