Using grapher or stats on a graph without paths raises error

[dubssieg]

Error TypeError: 'builtin_function_or_method' object is not iterable is happening when one try to compute cyclicity of graph:

│ ❱ 84 │ stats["Is graph acyclic"] = all([len(set([x for x, _ in path_datas["path"]])) == len │
│ 85 │ │ path_datas["path"]) for path_datas in graph.paths.values]) │

Needs some default value and error handling if no paths is provided.

[dubssieg]

This computation is now made within a try/except.