TransparencyManager: don't do transparency updates when transparency off
When all 4 transparency settings are set to zero (lockscreen/launcher
transparency for statusbar/navbar) there is no reason to process
transparency updates.
This also allows us to fall back to original getSystemDecorRectLw, which
will eliminate graphical glitch/anomaly appearing at the top of the
windows clearly visible during transition animations and/or in recent
apps dialog on some devices.