Fix crash when pausing work profile.

The issue happens when bindFastScrollbar is called during switching to a paused work tab and since there are no
letters to display (no sections in work tab because workProfile is paused) createVerticalChain complains because it needs two views to be
present when there are none. So just early check if there are sections existing will fix this.

bug:373533884
Test manually video: https://drive.google.com/file/d/1K9zdZthHNj4Gbdn-m30KINm3VFfwFfiM/view?usp=sharing
Flag: com.android.launcher3.letter_fast_scroller

Change-Id: I7a8501fa5e7d048fe5a2fe4525f96cc9809cfbfd