[Port] [BUG] adjacency_matrix fails for SimpleGraph with self-loops (Julia 1.7)

[gdalle]

See sbromberger/LightGraphs.jl#1594

[etiennedeg]

Fixed by #15

[gdalle]

@etienneINSA what is the rationale of allowing loops in a SimpleGraph? I'm all for a more explicit error message, but shouldn't this be forbidden from the start?

[etiennedeg]

In my understanding, SimpleGraphs (in the context of this library) allows self-loops (but no multiple edges), but I may be wrong... @jpfairbanks ?
If not, there is some work as there are no checks anywhere, and I have already encountered functions in the library which return graphs with self-loops.

[simonschoelly]

Self-loops where at one point allowed on purpose. And I would agree, while the strict mathematical definition of a simple graph does not allow self-loops, it is a nice feature to have.

One downside of that is though, that it adds additional edge cases that have to be checked for some algorithms.

[simonschoelly]

Fixed by #15