Make smallDateView optional in keyguard preview

Prevent crash when the view is not found.

Fixes: 424146059
Test: manual
Flag: com.android.systemui.shared.clock_reactive_smartspace_layout
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:cf61b7e56e19e2bedbb203e5d3fb425c7fc9953c)
Merged-In: Ieb4c777cc1b1a138928b85325b9f8a08f9f3d148
Change-Id: Ieb4c777cc1b1a138928b85325b9f8a08f9f3d148