VolumePreference.onActivityStop only stops playback

In VolumePreference.onActivityStop, the cleanup has
been replaced with only stopping ringtone playback
for the seekbar. This will avoid problems when switching
between applications that previously lead to inconsistencies
in the ring volume dialog.

Change-Id: Ia751fe0893610c4f5650eb07705481400642a84e

core/java/android/preference/VolumePreference.java

@@ -109,7 +109,9 @@ public class VolumePreference extends SeekBarPreference implements
     }
 
     public void onActivityStop() {
-        cleanup();
+        if (mSeekBarVolumizer != null) {
+            mSeekBarVolumizer.stopSample();
+        }
     }
 
     /**