readline: don't cache the "keypress" listeners

it's not safe to since `removeAllListeners()` will detach the returned
Array from the stream instance if that's ever called by the user.

lib/readline.js

@@ -786,10 +786,8 @@ function emitKeypressEvents(stream) {
   if (stream._emitKeypress) return;
   stream._emitKeypress = true;
 
-  var keypressListeners = stream.listeners('keypress');
-
   function onData(b) {
-    if (keypressListeners.length) {
+    if (stream.listeners('keypress').length > 0) {
       emitKey(stream, b);
     } else {
       // Nobody's watching anyway
@@ -805,7 +803,7 @@ function emitKeypressEvents(stream) {
     }
   }
 
-  if (keypressListeners.length) {
+  if (stream.listeners('keypress').length > 0) {
     stream.on('data', onData);
   } else {
     stream.on('newListener', onNewListener);