Fix NPE due to null clip descriptions

- Some apps start drags without clip descriptions, any logging should
  account for that as well

Flag: EXEMPT bugfix
Bug: 385901897
Test: atest WMShellUnitTests:DragAndDropControllerTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:00a6ab6442a94f3c0526f08f007ac8b068fb5682)
Merged-In: I0aaa9484b440bb0553d09e485f12759bf46c706b
Change-Id: I0aaa9484b440bb0553d09e485f12759bf46c706b