`findCycles` algorithm fails for undirected graphs

```javascript
let g = new graphlib.Graph({directed:false);                                           
g.setNode('1')
g.setNode('2')
g.setNode('3')
g.setEdge('1', '2')
g.setEdge('2', '3')
g.setEdge('1', '3')
console.log(graphlib.alg.findCycles(g))                                           
// expected: [ [ '1', '2', '3' ] ]
// got: [ ]
```