Ensure page scrolls are initialized even for 0 children.

Bug: 233713180
Test: Walk through CtsVerifier Lock Task UI flow as described in the bug
Change-Id: I49cb942a37a202b3e1b7ee00479d68402fcaf8b0
diff --git a/src/com/android/launcher3/PagedView.java b/src/com/android/launcher3/PagedView.java
index 4d33eae..73be5be 100644
--- a/src/com/android/launcher3/PagedView.java
+++ b/src/com/android/launcher3/PagedView.java
@@ -727,15 +727,16 @@
             pageScrollChanged = true;
         }
 
-        if (childCount == 0) {
-            return;
-        }
-
         if (DEBUG) Log.d(TAG, "PagedView.onLayout()");
 
         pageScrollChanged |= getPageScrolls(pageScrolls, true, SIMPLE_SCROLL_LOGIC);
         mPageScrolls = pageScrolls;
 
+        if (childCount == 0) {
+            onPageScrollsInitialized();
+            return;
+        }
+
         final LayoutTransition transition = getLayoutTransition();
         // If the transition is running defer updating max scroll, as some empty pages could
         // still be present, and a max scroll change could cause sudden jumps in scroll.