[ruby/irb] Fix bug infinite loop when pasting multilines fo code in Ruby 2.6

Fix bug infinite loop when pasting multilines fo code in Ruby 2.6.
This is not reproduced in Ruby 2.7.
Changes added in https://github.com/ruby/irb/pull/242/files#diff-612b926e42ed78aed1a889ac1944f7d22229b3a489cc08f837a7f75eca3d3399R155 are also reflected in Ruby 2.6.

https://github.com/ruby/irb/commit/0a77f75bf0

lib/irb/ruby-lex.rb

@@ -167,7 +167,7 @@ class RubyLex
           end
         end
       else
-        tokens = lexer.parse
+        tokens = lexer.parse.reject { |it| it.pos.first == 0 }
       end
     end
     tokens