- for metis-like graphs there is no guarantee that a zero-sized graph
has an offsets list with size 1 or size 0, so always use
numCells = max(0, xadj.size()-1)
this was already done in most places, but missed in the
decomposeGeneral method
STYLE: use sumOp<label>() instead of plusOp<label>()
0867816490