readline: return old status from _setRawMode

Return the previous raw mode setting from the internal `_setRawMode`
so that is easier to reset it to its original state later.

PR-URL: #6635
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: addaleax

lib/readline.js

@@ -183,9 +183,13 @@ Interface.prototype.setPrompt = function(prompt) {
 
 
 Interface.prototype._setRawMode = function(mode) {
+  const wasInRawMode = this.input.isRaw;
+
   if (typeof this.input.setRawMode === 'function') {
-    return this.input.setRawMode(mode);
+    this.input.setRawMode(mode);
   }
+
+  return wasInRawMode;
 };