Fix crash condition by adding a null check in DigitalWellBeingToast

Fixes a crash condition where TaskView#getRecentsView() could return null when being called from DigitalWellBeingToast#setBanner(), resulting in a crash.

Fixes: 217671133

Test: Manual
Change-Id: I964384d97d26336e9a5e8e4c025f66ab78c63e0a
diff --git a/quickstep/src/com/android/quickstep/views/DigitalWellBeingToast.java b/quickstep/src/com/android/quickstep/views/DigitalWellBeingToast.java
index 27a748d..79b15c7 100644
--- a/quickstep/src/com/android/quickstep/views/DigitalWellBeingToast.java
+++ b/quickstep/src/com/android/quickstep/views/DigitalWellBeingToast.java
@@ -306,7 +306,7 @@
 
     private void setBanner(@Nullable View view) {
         mBanner = view;
-        if (view != null) {
+        if (view != null && mTaskView.getRecentsView() != null) {
             setupAndAddBanner();
             setBannerOutline();
         }