iterate will not `break` if it's directly in the body

This is more like a bug in users code but... In the following code chunk, flowery won't `break` as expected.

```
library(flowery)

iter <- generator({
  for (x in letters) yield(x)
})

iterate(for(x in iter) {
  print(x)
  break
})
```

It's worth noting that this works as expected:

```
iterate(for(x in iter) {
  print(x)
  if (x == "b")
    break
})
```