core: Fix too long ON/OFF strings

Use Unicode chars '❙' for ON and '〇' for OFF

Change-Id: I563f1ea331a07dcaeedce28688c2121de0716185
systemui: Fix crash on theme change

 * Avoid NPE on theme change on devices without a navigation bar.

Change-Id: I29321e7747e7aa87f4539913b5a071f6e7d6a72d