Do less work on configuration change.

Change-Id: I8c657ba8913b4be288cb0979897479a1db33aacf
Fixes: 29625463

packages/SystemUI/src/com/android/systemui/volume/VolumeDialog.java

@@ -973,6 +973,7 @@ public class VolumeDialog implements TunerService.Tunable {
                 mDialog.dismiss();
                 mZenFooter.cleanup();
                 initDialog();
+                mDensity = density;
             }
             updateWindowWidthH();
             mSpTexts.update();