Fixed invalid synchronization impl, Closes android-async-http#730

Author: smarek

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

@@ -1309,9 +1309,10 @@ protected RequestHandle sendRequest(DefaultHttpClient client, HttpContext httpCo
         RequestHandle requestHandle = new RequestHandle(request);
 
         if (context != null) {
+            List<RequestHandle> requestList;
             // Add request to request map
-            List<RequestHandle> requestList = requestMap.get(context);
             synchronized (requestMap) {
+                requestList = requestMap.get(context);
                 if (requestList == null) {
                     requestList = Collections.synchronizedList(new LinkedList<RequestHandle>());
                     requestMap.put(context, requestList);