Release zlib callbacks and buffer after processing chunks

Author: mdlavin

lib/zlib.js

@@ -574,6 +574,13 @@ Zlib.prototype._processChunk = function(chunk, flushFlag, cb) {
   req.callback = callback;
 
   function callback(availInAfter, availOutAfter) {
+    if (this) {
+      // Don't hold onto the buffer and the callback
+      // after they have been used.
+      delete this.buffer;
+      delete this.callback;
+    }
+
     if (self._hadError)
       return;