Fix Storm Planner Bug

Verified the fix with some println debugging plus this:

```scala
object Test {
  import com.twitter.storehaus._
  import com.twitter.storehaus.algebra.MergeableStore
  import com.twitter.summingbird.storm._
  import com.twitter.summingbird._
  import com.twitter.summingbird.batch.{BatchID, Batcher}
  import com.twitter.tormenta.spout.Spout
 
  implicit val te = TimeExtractor[Int](i => i.toLong)
  implicit val batcher = Batcher.ofHours(1)
  val node = Storm.source(Spout.fromTraversable(Seq(1,2,3))).flatMap { i => List(i, i, i) }
 
  val newNode = node.flatMap(i => Some(i)).write(() => _ => com.twitter.util.Future.Unit)
 
  try {
    Storm.local("face").plan {
      node.either(newNode).flatMap {
        case Left(t) => Some(t)
        case Right(r) => None
      }.map(_ -> 1L).sumByKey {
        MergeableStoreSupplier.from {
          MergeableStore.fromStore[(Int, BatchID), Long](new JMapStore())
        }
      }
    }
  } catch {
    case _ => null
  }
}
```