frameworks: allow LockPatternView to be rotated

When displaying this view and rotating the screen, mLockPatternUtils has
the potential to be null, but the save and restore instance state
methods depend on it to be initialized. Work around this by checking if
it's null.

Change-Id: I351bd63fefbcb92fffe20dca6a0381a20ac796ea
Signed-off-by: Roman Birg <roman@cyngn.com>