Fix java crash by inconsistent single-line view and view model

Fix the java crash when a conversation notification entry has null
MessagingStyle.

Fix: 368441586
Flag: com.android.systemui.notification_async_hybrid_view_inflation
Test: SingleLineViewBinderTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:8702b2246c3282abe105d2e60ca4f74d57d11e09)
Merged-In: If47e3f0ccfcc5e7079189288a6f3820691abd3e8
Change-Id: If47e3f0ccfcc5e7079189288a6f3820691abd3e8