Refresh wallpaper section and update category fragment

Refresh wallpaper section in CustomizationPickerActivity's onResume()
and update its fragment for the preview changing.

Bug: 131811513
Test: Manual
Change-Id: Ide89f944d908fd034b1bbf05d1322961f429881e
diff --git a/src/com/android/customization/picker/CustomizationPickerActivity.java b/src/com/android/customization/picker/CustomizationPickerActivity.java
index 8759dab..281ff78 100644
--- a/src/com/android/customization/picker/CustomizationPickerActivity.java
+++ b/src/com/android/customization/picker/CustomizationPickerActivity.java
@@ -141,6 +141,18 @@
         mUserEventLogger.logResumed();
         // refresh the sections as the preview may have changed
         initSections();
+        if (mBottomNav == null) {
+            return;
+        }
+        CustomizationSection section = mSections.get(mBottomNav.getSelectedItemId());
+        if (section == null) {
+            return;
+        }
+        // Keep CategoryFragment's design to load category within its fragment
+        if (section instanceof WallpaperSection) {
+            switchFragment(section);
+            section.onVisible();
+        }
     }
 
     @Override