Fix SFLayer TypeErrors in Winscope

Fix the errors that pop up when clicking `SurfaceFlingerLayer` in
SurfaceFlingerTrace panel's Hierarchy panel, by taking care of cases
where the property is null.

Bug: 240405932
Test: manual on local build of Winscope
Change-Id: Ic9e8f6e75dcfde8af97aeb5254d1e2d8f7b3d669
2 files changed