AdaptorService crashes if there are no adaptors

[stuartc]

** (Mix) Could not start application open_fn: OpenFn.start(:normal, []) returned an error: shutdown: failed to start child: Engine.Adaptor.Service
    ** (EXIT) an exception was raised:
        ** (File.Error) could not read file "package.json": no such file or directory
            (elixir 1.11.4) lib/file.ex:355: File.read!/1
            (engine 0.3.1) lib/engine/adaptor/repo.ex:12: anonymous fn/1 in Engine.Adaptor.Repo.list_local/2
            (elixir 1.11.4) lib/enum.ex:1411: Enum."-map/2-lists^map/1-0-"/2
            (engine 0.3.1) lib/engine/adaptor/service.ex:85: Engine.Adaptor.Service.State.refresh_list/1
            (engine 0.3.1) lib/engine/adaptor/service.ex:98: Engine.Adaptor.Service.start_link/1
            (stdlib 3.14.2.2) supervisor.erl:385: :supervisor.do_start_child_i/3
            (stdlib 3.14.2.2) supervisor.erl:371: :supervisor.do_start_child/2
            (stdlib 3.14.2.2) supervisor.erl:355: anonymous fn/3 in :supervisor.start_children/2