Avoid possible NPE on getTag if no was set before

Author: smarek

library/src/main/java/com/loopj/android/http/RequestHandle.java

@@ -27,7 +27,7 @@
  */
 public class RequestHandle {
     private final WeakReference<AsyncHttpRequest> request;
-    private WeakReference<Object> TAG = null;
+    private WeakReference<Object> TAG = new WeakReference<Object>(null);
 
     public RequestHandle(AsyncHttpRequest request) {
         this.request = new WeakReference<AsyncHttpRequest>(request);