Handle edgeless graphs.
Handle edgeless graphs.

As title.

numba/numba,stonebig/numba,seibert/numba,stonebig/numba,gmarkall/numba,cpcloud/numba,IntelLabs/numba,IntelLabs/numba,gmarkall/numba,IntelLabs/numba,IntelLabs/numba,cpcloud/numba,numba/numba,seibert/numba,stuartarchibald/numba,cpcloud/numba,numba/numba,seibert/numba,stonebig/numba,stuartarchibald/numba,stuartarchibald/numba,numba/numba,IntelLabs/numba,stuartarchibald/numba,gmarkall/numba,stuartarchibald/numba,gmarkall/numba,cpcloud/numba,gmarkall/numba,seibert/numba,seibert/numba,stonebig/numba,numba/numba,cpcloud/numba,stonebig/numba