Fix Encoding::ConverterNotFoundError

[koic]

Follow #237.

This PR fixes the following Encoding::ConverterNotFoundError.

% bin/spring stop && bin/rails c
Spring stopped.
Running via Spring preloader in process 58395
Loading development environment (Rails 6.0.3.7)
irb(main):001:0> "こんにちは".do_something
Traceback (most recent call last):
(snip)

    12: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:547:in `eval_input'
    11: from /Users/koic/src/github.com/ruby/irb/lib/irb/ruby-lex.rb:232:in `each_top_level_statement'
    10: from /Users/koic/src/github.com/ruby/irb/lib/irb/ruby-lex.rb:232:in `catch'
     9: from /Users/koic/src/github.com/ruby/irb/lib/irb/ruby-lex.rb:233:in  `block in each_top_level_statement'
     8: from /Users/koic/src/github.com/ruby/irb/lib/irb/ruby-lex.rb:233:in `loop'
     7: from /Users/koic/src/github.com/ruby/irb/lib/irb/ruby-lex.rb:251:in `block (2 levels) in each_top_level_statement'
     6: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:548:in `block in eval_input'
     5: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:758:in `signal_status'
     4: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:586:in `block (2 levels) in eval_input'
     3: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:650:in `handle_exception'
     2: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:601:in `encode_with_invalid_byte_sequence'
     1: from /Users/koic/src/github.com/ruby/irb/lib/irb.rb:601:in `new'
/Users/koic/src/github.com/ruby/irb/lib/irb.rb:601:in `initialize': code
converter not found (UTF-8 to UTF-8) (Encoding::ConverterNotFoundError)

First, this patch skips Encoding::Converter.new for the same encoding.

irb/lib/irb.rb

Line 601 in 170531d

conv = Encoding::Converter.new(str.encoding, enc)

Next, this is a talk about the condition for skipping. IRB.conf[:LC_MESSAGES].encoding becomes "UTF-8" string when Reline.encoding_system_needs.name is set in the below.

irb/lib/irb/input-method.rb

Line 269 in 170531d

IRB.__send__(:set_encoding, Reline.encoding_system_needs.name, override: false)

OTOH, message.encoding is Encoding::UTF_8, so these are compared as a string by this patch.

[aycabta]

Great!