proper backpressure on backend's next()

Author: James Halliday

index.js

@@ -73,10 +73,9 @@ Backend.prototype._read = function (n) {
 Backend.prototype._write = function (buf, enc, next) {
     if (this._stream) {
         this._stream.push(buf);
-        next();
     }
     else {
         this._buffer = buf;
-        this._next = next;
     }
+    this._next = next;
 };