Fixes minimized state in DividerController when dismissing docked stack

When dismiss docked stack is dimissed without going back to multiwindow
mode, it will not set the mMinimizedDock to false. It will then assume
all interactions as minimized mode. Some issues occur such as trying to
go back into multiwindow mode will fail (leave the docked task docked
while launcher is shown behind it). It is possible to trigger a docked
stack dimissal with Activity.finish() from an app while in minimized
mode.

Test: manual - manually dismissed dock stack and tried to go back into
multiwindow mode
Change-Id: I2a8af3e6b9ea70a85e89adc7be50f31527af5c80