clist: non-deterministic test failure

Happened in unrelated PR:
- https://github.com/tendermint/tendermint/pull/2205/
- https://circleci.com/gh/tendermint/tendermint/20143#tests/containers/3

```
--- FAIL: TestWaitChan (1.26s)
	clist_test.go:271: number of pushed items (99) not equal to number of seen items (98)
```