CallStyle: Also handle null label to glue

Bug: <329288442>
Flag: ACONFIG com.android.systemui.new_call_style_action_layout NEXTFOOD
Test: none
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:614da108d8e4259ad925a437830408e83b6c3979)
Merged-In: Ib8958198aa7e99b0db54834602ecf4767146c560
Change-Id: Ib8958198aa7e99b0db54834602ecf4767146c560
24D1-dev is based on 24Q2-release. Therefore, we merged this CL to 24D1-dev.