Add null-check for system audio mode change event.

Bug: 17270923
Change-Id: I23fa593893591f6032105ff936b8eee10d8c0cfa
diff --git a/services/core/java/com/android/server/tv/TvInputHardwareManager.java b/services/core/java/com/android/server/tv/TvInputHardwareManager.java
index fa991c2..77ab33b 100644
--- a/services/core/java/com/android/server/tv/TvInputHardwareManager.java
+++ b/services/core/java/com/android/server/tv/TvInputHardwareManager.java
@@ -1021,7 +1021,9 @@
             synchronized (mLock) {
                 for (int i = 0; i < mConnections.size(); ++i) {
                     TvInputHardwareImpl impl = mConnections.valueAt(i).getHardwareImplLocked();
-                    impl.handleAudioSinkUpdated();
+                    if (impl != null) {
+                        impl.handleAudioSinkUpdated();
+                    }
                 }
             }
         }