Graceful error handling for missing chats

[Voronchuk]

Error log for debugging:

[error] GenServer Instafoto.Bot.Telegram terminating
** (WithClauseError) no with clause matching: {:error, %Nadia.Model.Error{reason: "Bad Request: chat not found"}}
    (botlead) lib/botlead/bot/adapter/telegram.ex:35: Botlead.Bot.Adapter.Telegram.send_message/4
    (instafoto) lib/instafoto/bot/telegram.ex:6: Instafoto.Bot.Telegram.handle_cast/2
    (stdlib) gen_server.erl:637: :gen_server.try_dispatch/4
    (stdlib) gen_server.erl:711: :gen_server.handle_msg/6
    (stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Last message: {:"$gen_cast", {:send_message, "185145043", "*Shoot* from Viacheslav V.: 0,-\n\n0, flexible time\n\n\n\n\n", [parse_mode: "Markdown", reply_markup: %{inline_keyboard: [[%{callback_data: "/invites/41/accept", text: "Accept"}, %{callback_data: "/invites/41/decline", text: "Decline"}]]}]}}
State: %{clients: %{}, last_update: 0, listener: nil, poll_delay: 600, poll_limit: 100, poll_timer: #Reference<0.3203458176.2576351235.214485>, processed_messages: []}
[info] Starting polling of Telegram bot updates...