Reproduction steps:
1. Open the attached project;
2. Open the scene "test";
3. Enter Play mode;
4. Click on "Helper" -> "State Sequence" -> a button "Clear";

Actual result: Unity crashes in <StopCoroutineFromEnumeratorManaged>.
Expected result: Unity should not crash.

Note: the crash happens because of the function StopCoroutine which in the foreach loop. When the function is commented in StateSequence.cs 96 line, Unity does not crash.

Reproduced with: 5.5.2f1, 5.5.2p3
Not reproducible with: 5.5.0a6, 5.5.1f1
Regression introduced in 5.5.2f1