Fix black Keyguard

When a window has both the flag fullscreen and the dismiss Keyguard
flag, we end up in a state where we hide the status bar window but
all other windows, because mShowingLockscreen nevers gets set
correctly. Move it up so we always set it no matter whether the
status bar window was visible.

Bug: 22875357
Change-Id: I7953fe7100cc99fe8fb7424a9b311b4630426657