Optimize FromIterable

When the Collection to be emitted is smaller than the buffer size it skips the setProducer logic.

Before this change:

```
Run: 10 - 9,023,397 ops/sec
Run: 11 - 9,238,728 ops/sec
Run: 12 - 9,279,881 ops/sec
Run: 13 - 9,367,769 ops/sec
Run: 14 - 9,226,283 ops/sec
```

After:

```
Run: 10 - 9,792,401 ops/sec
Run: 11 - 9,838,259 ops/sec
Run: 12 - 9,942,532 ops/sec
Run: 13 - 10,051,160 ops/sec
Run: 14 - 10,263,884 ops/sec
```