error when game is started with no snakes

[Dkendal]

I consider this to be an edge case, and because the game dies in isolation i am totally okay with it.

Steps to recreate

• create new game with no snakes in it

• starts the game

• [error] GenServer {BattleSnake.GameServer.Registry, "aeab10d7-adce-43af-b270-767a8775c2a8"} terminating

  [error] GenServer {BattleSnake.GameServer.Registry, "aeab10d7-adce-43af-b270-767a8775c2a8"} terminating
  ** (Enum.EmptyError) empty error
      (elixir) lib/enum.ex:1386: anonymous fn/0 in Enum.max_by/2
      (battle_snake) lib/battle_snake/rules.ex:17: BattleSnake.Rules.do_last_standing/1
      (elixir) lib/map.ex:646: Map.update!/3
      (elixir) lib/enum.ex:1755: Enum."-reduce/3-lists^foldl/2-0-"/3
      (battle_snake) lib/battle_snake/game_server/server.ex:110: BattleSnake.GameServer.Server.handle_info/2
      (stdlib) gen_server.erl:601: :gen_server.try_dispatch/4
      (stdlib) gen_server.erl:667: :gen_server.handle_msg/5
      (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
  Last message: :tick
  State: %BattleSnake.GameServer.State{delay: 100, game_form: %BattleSnake.GameForm{__meta__: #Ecto.Schema.Metadata<:built, "gam
  e">, delay: 100, game_mode: "singleplayer", height: 20, id: "aeab10d7-adce-43af-b270-767a8775c2a8", max_food: 4, snakes: [], width: 20, winners: [%BattleSnake.Snake{color: "", coords: [%BattleSnake.Point{x: 6, y: -1}, %BattleSnake.Point{x: 6, y: 0}, %BattleSnake.Point{x: 6, y: 1}], head_url: "", health: {:error, {:invalid, "<"}}, health_points: 97, id: "8ed9aa9b-d730-46cc-a7b0-76e29b2fcc99", name: "", taunt: nil, url: "localhost:4000"}], world: %BattleSnake.World{created_at: nil, dead_snakes: [], deaths: [], food: [%BattleSnake.Point{x: 3, y: 3}, %BattleSnake.Point{x: 16, y: 5}, %BattleSnake.Point{x: 17, y: 15}, %BattleSnake.Point{x: 14, y: 2}], game_form_id: "aeab10d7-adce-43af-b270-767a8775c2a8", game_id: "aeab10d7-adce-43af-b270-767a8775c2a8", height: 20, id: nil, max_food: 4, moves: %{}, snakes: [], turn: 0, width: 20}}, game_form_id: "aeab10d7-adce-43af-b270-767a8775c2a8", hist: [], objective: #Function<1.31983054/1 in BattleSnake.WinConditions.game_mode/1>, on_change: #Function<7.18877502/1 in BattleSnake.GameForm.to_game_server_state/1>, on_done: #Function<8.18877502/1 in BattleSnake.GameForm.to_game_server_state/1>, on_start: &BattleSnake.GameServer.State.identity/1, status: :cont, winners: [], world: %BattleSnake.World{created_at: nil, dead_snakes: [], deaths: [], food: [%BattleSnake.Point{x: 3, y: 3}, %BattleSnake.Point{x: 16, y: 5}, %BattleSnake.Point{x: 17, y: 15}, %BattleSnake.Point{x: 14, y: 2}], game_form_id: "aeab10d7-adce-43af-b270-767a8775c2a8", game_id: "aeab10d7-adce-43af-b270-767a8775c2a8", height: 20, id: nil, max_food: 4, moves: %{}, snakes: [], turn: 0, width: 20}}