Hash table can be overloaded and never returns from a insertion

[Akatsukis]

gbbs/gbbs/contract.h

Line 43 in 3491d54

sequence<edge_entry> fetch_intercluster_small(Graph& GA, C& clusters,

In this function, if the number of distinct edges is greater than small_cluster_size, the hash table can be fully inserted and never returns. In my opinion, the coarsening should base on the number of edges instead of the number of clusters.