Vibration mode is not set even slider is moved to left most side

Ringer mode is not changed from normal to vibrate when slider is moved
to left most side from ringer volume preference dialog or volume
control bar. It also fixes the issue where current ringer mode is
silent and ringer volume prefernce dialog is closed without changing
anything resulting mode change to vibrate.

Change-Id: Ia4e454ad9ebc890e4854d62168e9ac8beada040f