.<TAB> autocomplete fails in 1.10+ for variables ending with a Unicode character

[pablosanjose]

In v1.10+, using .<TAB> to find a variable's field names errors if the variable name ends in a Unicode character.

Demo

julia> struct T; x::Int; end

julia> β = T(1)

julia> β.<TAB>┌ Error: Error in the keymap
│   exception =
│    StringIndexError: invalid index [2], valid nearby indices [1]=>'α', [3]=>'.'
│    Stacktrace:
│      [1] string_index_err(s::String, i::Int64)
│        @ Base ./strings/string.jl:12
│      [2] getindex
│        @ Base ./strings/string.jl:470 [inlined]
│      [3] complete_identifiers!(suggestions::Vector{REPL.REPLCompletions.Completion}, ffunc::Function, context_module::Module, string::String, name::String, pos::Int64, dotpos::Int64, startpos::Int64, comp_keywords::Bool)
│        @ REPL.REPLCompletions /Applications/Julia-1.10.app/Contents/Resources/julia/share/julia/stdlib/v1.10/REPL/src/REPLCompletions.jl:946
│      [4] completions(string::String, pos::Int64, context_module::Module, shift::Bool)
│        @ REPL.REPLCompletions /Applications/Julia-1.10.app/Contents/Resources/julia/share/julia/stdlib/v1.10/REPL/src/REPLCompletions.jl:1166
│      [5] complete_line(c::REPL.REPLCompletionProvider, s::REPL.LineEdit.PromptState, mod::Module)
...

With β2 = T(2) the .<TAB> correctly autocompletes to β2.x, as in 1.9.