check null pointer on mNetworkAgent

Bug:16776614

Change-Id: I6af588a0bc7f9048174d359f41f63ac9acb98147
diff --git a/service/java/com/android/server/wifi/WifiStateMachine.java b/service/java/com/android/server/wifi/WifiStateMachine.java
index 107f720..2bf4a39 100644
--- a/service/java/com/android/server/wifi/WifiStateMachine.java
+++ b/service/java/com/android/server/wifi/WifiStateMachine.java
@@ -2944,7 +2944,9 @@
                 loge("calculateWifiScore() report new score " + Integer.toString(score));
             }
             mWifiInfo.score = score;
-            mNetworkAgent.sendNetworkScore(score);
+            if (mNetworkAgent != null) {
+                mNetworkAgent.sendNetworkScore(score);
+            }
         }
     }