Fix crash when no behaviours

Author: lukaszsamson

lib/elixir_sense/core/compiler.ex

@@ -1802,7 +1802,7 @@ defmodule ElixirSense.Core.Compiler do
     # elixir forces runtime dependency on behaviour via Module.force_behaviour_dependencies
     # which emits a trace for a fake behaviour_info call
     state =
-      Enum.reduce(state.behaviours[full], state, fn behaviour, state ->
+      Enum.reduce(Map.get(state.behaviours, full, []), state, fn behaviour, state ->
         state
         |> State.add_call_to_line(
           {behaviour, :behaviour_info, 1},