Do not generate unnecessary db queries

[do4gr]

I stumbled over cases where we do requests for related nodes even though we did not find a parent node.

      s"""
         |model User {
         |  id       Int     @id
         |  name     String?
         |  postId   Int?
         |  post2Id  Int?
         |  post     Post?   @relation( fields: [postId], references: [id])
         |  post2    Post2?  @relation( fields: [post2Id], references: [id])
         |}
         |
         |model Post {
         |  id       Int     @id
         |  name     String?
         |  user     User?
         |}         
         |
         |model Post2 {
         |  id       Int     @id
         |  name     String?
         |  user     User?
         |}         
         |
         |
       """.stripMargin
    }
    database.setup(project)

    val find_1 = server.query(
      """
        |query {
        |  users(where: {id: 5 }){
        |    id
        |    name
        |    post  {name}
        |    post2 {name}
        |  }
        |}
      """,
      project
    )

    find_1.toString should be("{\"data\":{\"users\":[]}}")

Since I created no nodes, only the top level should be queried from the db. But the following SQL statements are sent:

The last two are unnecessary. Hint from @dom the place to catch that would be in nested read if joined_projections are empty.