Show minimum volume when the stream is updated with muted state

This makes the behaviour consistent with the Volume Panel.

Flag: com.android.systemui.volume_redesign
Fixes: 418101670
Test: atest VolumeDialogScreenshotTest
Test: manual on foldable. Change ringer mode and observe the ring
slider.

Change-Id: I520408575bf77650f4a50c2e8c7c798b89c0df6e