Settings: Make SeekBarVolumizer more null-resilient.

Now that the instances are reusable, ensure all "post" methods
do a handler check, and ensure they are all internal.

Bug: 18063070
Change-Id: Idc478c636686f666f5656f3d07bf2738ba3e9a5a

core/java/android/preference/SeekBarVolumizer.java

@@ -130,6 +130,7 @@ public class SeekBarVolumizer implements OnSeekBarChangeListener, Handler.Callba
     }
 
     private void postStartSample() {
+        if (mHandler == null) return;
         mHandler.removeMessages(MSG_START_SAMPLE);
         mHandler.sendMessageDelayed(mHandler.obtainMessage(MSG_START_SAMPLE),
                 isSamplePlaying() ? CHECK_RINGTONE_PLAYBACK_DELAY_MS : 0);
@@ -150,7 +151,8 @@ public class SeekBarVolumizer implements OnSeekBarChangeListener, Handler.Callba
         }
     }
 
-    void postStopSample() {
+    private void postStopSample() {
+        if (mHandler == null) return;
         // remove pending delayed start messages
         mHandler.removeMessages(MSG_START_SAMPLE);
         mHandler.removeMessages(MSG_STOP_SAMPLE);
@@ -200,7 +202,8 @@ public class SeekBarVolumizer implements OnSeekBarChangeListener, Handler.Callba
         postSetVolume(progress);
     }
 
-    void postSetVolume(int progress) {
+    private void postSetVolume(int progress) {
+        if (mHandler == null) return;
         // Do the volume changing separately to give responsive UI
         mLastProgress = progress;
         mHandler.removeMessages(MSG_SET_STREAM_VOLUME);

core/java/android/preference/VolumePreference.java

@@ -117,7 +117,7 @@ public class VolumePreference extends SeekBarDialogPreference implements
 
     public void onActivityStop() {
         if (mSeekBarVolumizer != null) {
-            mSeekBarVolumizer.postStopSample();
+            mSeekBarVolumizer.stopSample();
         }
     }