Errors when using Unicode string

```
julia> using Reduce
Reduce (Free CSL version, revision 5286), 01-Mar-20 ...
REPL mode REDUCE initialized. Press } to enter and backspace to exit.

reduce> α;
ERROR: StringIndexError("α;", 2)
Stacktrace:
[1] string_index_err(::String, ::Int64) at ./strings/string.jl:12
[2] getindex at ./strings/string.jl:250 [inlined]
[3] parserepl(::String) at /Users/tomyun/.julia/packages/Reduce/fWMAZ/src/repl.jl:32
[4] #invokelatest#1 at ./essentials.jl:712 [inlined]
[5] invokelatest at ./essentials.jl:711 [inlined]
[6] (::REPL.var"#do_respond#38"{Bool,typeof(Reduce.parserepl),REPL.LineEditREPL,REPL.LineEdit.Prompt})(::Any, ::Any, ::Any) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/REPL/src/REPL.jl:724
[7] #invokelatest#1 at ./essentials.jl:712 [inlined]
[8] invokelatest at ./essentials.jl:711 [inlined]
[9] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/REPL/src/LineEdit.jl:2354
[10] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/REPL/src/REPL.jl:1055
[11] run_repl(::REPL.AbstractREPL, ::Any) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/REPL/src/REPL.jl:206
[12] (::Base.var"#764#766"{Bool,Bool,Bool,Bool})(::Module) at ./client.jl:383
[13] #invokelatest#1 at ./essentials.jl:712 [inlined]
[14] invokelatest at ./essentials.jl:711 [inlined]
[15] run_main_repl(::Bool, ::Bool, ::Bool, ::Bool, ::Bool) at ./client.jl:367
[16] exec_options(::Base.JLOptions) at ./client.jl:305
[17] _start() at ./client.jl:484
```

On the other hand, running the same statement via `rcall()` seems to work fine.

```
julia> "α;" |> rcall
"!#03b1;"

julia> ans |> RExpr

α
```

In the meantime, calling a similar statement can make my REPL stuck indefinitely.

```
julia> "αα;" |> rcall

# no response
```