Fix autocomplete crash when expanding struct with __MODULE__

[lukaszsamson]

This PR fixes

*** ERROR: Shell process terminated! (^G to start new job) ***

21:39:55.166 [error] Process #PID<0.70.0> raised an exception
** (FunctionClauseError) no function clause matching in Module.concat/2
    (elixir 1.18.2) lib/module.ex:961: Module.concat(Elixir, {:__MODULE__, [line: 1], nil})
    (iex 1.18.2) lib/iex/autocomplete.ex:471: IEx.Autocomplete.value_from_alias/2
    (iex 1.18.2) lib/iex/autocomplete.ex:422: IEx.Autocomplete.container_context_struct/4
    (iex 1.18.2) lib/iex/autocomplete.ex:334: IEx.Autocomplete.expand_container_context/4
    (iex 1.18.2) lib/iex/autocomplete.ex:82: IEx.Autocomplete.expand_code/2
    (kernel 9.2.4.6) group.erl:685: :group.get_line1/5
    (kernel 9.2.4.6) group.erl:517: :group.get_chars_loop/10
    (kernel 9.2.4.6) group.erl:213: :group.io_request/6
iex(1)> %__MODULE__.Sd{

[josevalim]

Can we also have a test? Thank you!

[lukaszsamson]

Sure. I thought it's not worth covering this case as completions do not return anything useful.

[josevalim]

But given it raises, we should double check it at least returns nothing!

[lukaszsamson]

Done

[josevalim]

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