I have defined a simple graph that combines a constant stream (defined via `Source.Single(5000)`) with a source that is non-constant (e.g. `Source(1 to 100)`). My graph adds the two numbers together via a `ZipLatestWith` operator. The intention is for the output of the stream to be `5001, 5002, 5003, 5004, ..., 5100`. In reality the output of the program is simply `5000`, and then the stream terminates presumably because the `Single` source completes.

How do I get the expected result, where the source with the constant value of `5000` is combined with every value of the non-constant source? Note that due to conceptual reasons (irrelevant to this specific example), it's important that the constant source remains a source of the stream. A complete code example is as follows, which simply prints the number `5000` to the console.

Main.scala: 

```
import akka.NotUsed
import akka.actor.typed.scaladsl.Behaviors
import akka.actor.typed.{ActorSystem, Behavior, Terminated}
import akka.stream.scaladsl.{Flow, GraphDSL, Sink, Source, ZipLatestWith}
import akka.stream.{FlowShape, Materializer}

object Main {
  def apply(): Behavior[NotUsed] = {
    Behaviors.setup { context =>

      val constantStream: Source[Int, NotUsed] = Source.single(5000)
      val graph: Flow[Int, Int, NotUsed] = Flow.fromGraph(GraphDSL.create(){
        implicit builder =>
          import GraphDSL.Implicits._

          val zipper = builder.add(ZipLatestWith[Int, Int, Int]((a: Int, b: Int) => a * b))
          constantStream ~> zipper.in1

          FlowShape(zipper.in0, zipper.out)
      })

      Source(1 to 100)
        .via(graph)
        .to(Sink.foreach(println)).run()(Materializer.apply(context))

      Behaviors.receiveSignal {
        case (_, Terminated(_)) =>
          Behaviors.stopped
      }
    }
  }

  def main(args: Array[String]): Unit = {
    ActorSystem(Main(), "test")
  }
}

```

build.sbt: 

```
scalaVersion := "2.12.6"
libraryDependencies += "com.typesafe.akka" %% "akka-actor-typed" % "2.6.0"
libraryDependencies += "com.typesafe.akka" %% "akka-stream-typed" % "2.6.0"
libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.2.3"

```