Dependency cycle detection algorithm sometimes fails

[denisdefreyne]

Steps to reproduce

Call #any_cycle on a graph with the following edges:

[
[1, 52, nil],
[50, 0, nil],
[50, 1, nil],
[50, 2, nil],
[50, 3, nil],
[50, 4, nil],
[50, 5, nil],
[50, 6, nil],
[50, 7, nil],
[50, 8, nil],
[50, 9, nil],
[50, 10, nil],
[50, 11, nil],
[50, 12, nil],
[50, 13, nil],
[50, 14, nil],
[50, 15, nil],
[50, 16, nil],
[50, 17, nil],
[50, 18, nil],
[50, 19, nil],
[50, 20, nil],
[50, 21, nil],
[50, 22, nil],
[50, 23, nil],
[50, 24, nil],
[50, 25, nil],
[50, 26, nil],
[50, 27, nil],
[50, 28, nil],
[50, 29, nil],
[50, 30, nil],
[50, 31, nil],
[50, 32, nil],
[50, 33, nil],
[50, 34, nil],
[50, 35, nil],
[50, 36, nil],
[50, 37, nil],
[50, 38, nil],
[50, 39, nil],
[50, 40, nil],
[50, 41, nil],
[50, 42, nil],
[50, 43, nil],
[50, 44, nil],
[50, 45, nil],
[50, 46, nil],
[50, 47, nil],
[50, 48, nil],
[50, 49, nil],
[51, 50, nil],
[52, 51, nil]
]

Expected behavior

#any_cycle returns a cycle.

Actual behavior

#any_cycle returns nil.