Fix NPE

"should never happen", but... is

Test: NotificationEntryTest
Fixes: 444767151
Flag: com.android.systemui.notification_bundle_ui
(cherry picked from commit 999d28638cbc943a33127a49c8009cdc83e63748)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:62a887ef8c22f8e05304134e582b0fcc7698a642
Merged-In: Ib8c9c9caec94b9e5cf8f39d53f3615c54b6093ba
Change-Id: Ib8c9c9caec94b9e5cf8f39d53f3615c54b6093ba