repl: try setting the readline output on carriage return

If the first "input" is a StringIO, so the old approach never sets the
realine output, so we have to check every time.

lib/pry/repl.rb

@@ -26,10 +26,6 @@ def initialize(pry, options = {})
       if options[:target]
         @pry.push_binding options[:target]
       end
-
-      if readline_available? && piping?
-        Readline.output = File.open('/dev/tty', 'w')
-      end
     end
 
     # Start the read-eval-print loop.
@@ -184,6 +180,7 @@ def read_line(current_prompt)
         end
 
         if readline_available?
+          set_readline_output
           input_readline(current_prompt, false) # false since we'll add it manually
         elsif coolline_available?
           input_readline(current_prompt)
@@ -222,5 +219,11 @@ def coolline_available?
     def piping?
       !$stdout.tty? && $stdin.tty? && !Pry::Helpers::BaseHelpers.windows?
     end
+
+    def set_readline_output
+      @readline_output ||= if piping?
+                             Readline.output = File.open('/dev/tty', 'w')
+                           end
+    end
   end
 end