Always report mandatory insets for button nav

Fixes: 340134342
Test: atest android.systemui.cts.WindowInsetsBehaviorTests
Change-Id: Iee9d5ca9f12ff63f856e7aa94227e5b8273e02a4
diff --git a/quickstep/src/com/android/launcher3/taskbar/TaskbarInsetsController.kt b/quickstep/src/com/android/launcher3/taskbar/TaskbarInsetsController.kt
index 4f511c1..6869ecd 100644
--- a/quickstep/src/com/android/launcher3/taskbar/TaskbarInsetsController.kt
+++ b/quickstep/src/com/android/launcher3/taskbar/TaskbarInsetsController.kt
@@ -223,7 +223,7 @@
             provider.insetsSize = getInsetsForGravityWithCutout(contentHeight, gravity, endRotation)
         } else if (provider.type == mandatorySystemGestures()) {
             if (context.isThreeButtonNav) {
-                provider.insetsSize = Insets.of(0, 0, 0, 0)
+                // Leave null to inset by the window frame
             } else {
                 val gestureHeight =
                         ResourceUtils.getNavbarSize(