Fixes crash when pinning unfocused task in multiwindow

If an app can invoke pin locked mode such as Play video, and is split to
the bottom/right and not focused (focus the primary split task), then it
will crash trying to start lock task mode. Fix by moving pinned task to
front to become focused.

Change-Id: Ifd2c91b90d0f9f29111321f6fb2a1c5cf0073c49
Fixes: 72868672
Test: manual