[erlc] internal error in pass beam_kernel_to_ssa (fun expression with convoluted scoping)

[RobinMorisset]

On master, the following test case crashes erlc:

f() ->
    {
        (case [] of
            #{} ->
                X = 0;
            X ->
                0
        end),
        fun X() ->
            X
        end
    }.

with the following error message:

Function: f/0
minimized/kernel.erl: internal error in pass beam_kernel_to_ssa:
exception error: bad key: 'X'
  in function  map_get/2
     called as map_get('X',#{0 => {b_var,0},'@ssa_ret' => {b_var,'@ssa_ret'}})
     *** argument 1: not present in map
  in call from beam_kernel_to_ssa:ssa_arg/2 (beam_kernel_to_ssa.erl, line 1127)
  in call from beam_kernel_to_ssa:'-internal_cg/5-lc$^0/1-0-'/2 (beam_kernel_to_ssa.erl, line 1125)
  in call from beam_kernel_to_ssa:'-internal_cg/5-lc$^0/1-0-'/2 (beam_kernel_to_ssa.erl, line 1125)
  in call from beam_kernel_to_ssa:internal_cg/5 (beam_kernel_to_ssa.erl, line 1125)
  in call from beam_kernel_to_ssa:cg/2 (beam_kernel_to_ssa.erl, line 113)
  in call from beam_kernel_to_ssa:do_match_cg/3 (beam_kernel_to_ssa.erl, line 167)
  in call from beam_kernel_to_ssa:cg_fun/2 (beam_kernel_to_ssa.erl, line 91)