Deleting a self loop makes stinger go into an infinite loop.

[rohitvarkey]

Discovered in stingergraph/StingerGraphs.jl#5.

I discussed this with @jpfairbanks and @ehein6 today and we understood that it probably occurs due to this note specified in the definition of stinger_remove_edge.

A simple code snippet to reproduce this behavior is given below. I've also added this as part of the stinger_core_test.cpp file here

stinger_insert_edge(S, 0, 300, 300, 1, 1);
stinger_remove_edge(S, 0, 300, 300); //Goes into an infinite loop.