Adjusted find_neighbor_pores and find_neighbor_throats to return an empty nd array if they receive an empty nd array
Adjusted find_neighbor_pores and find_neighbor_throats to return an empty nd array if they receive an empty nd array

PMEAL/OpenPNM,amdouglas/OpenPNM,stadelmanma/OpenPNM,TomTranter/OpenPNM,amdouglas/OpenPNM