Dismiss lingering volume dialog

(1) Fault tolerance for the state where the dialog is not showing but
mShowing flag is set to false.

(2) Extra logging for better understanding the state of the dialog.

Bug: b/232606092

Test: Manual. Open volume dialog, adjust using volume buttons. Slider
should move smoothly and eventually dialog should dismiss smoothly.

Change-Id: Ie914f97925d8defb8c57818e5e7ffe958936336c