Fix NPE inside getFocusdChild

Bug: 172883035
Change-Id: Iea3e07165cdaa45031ee5bbc11add5c115cab366
diff --git a/src/com/android/launcher3/allapps/AlphabeticalAppsList.java b/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
index 2450787..354f97c 100644
--- a/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
+++ b/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
@@ -132,6 +132,9 @@
      * Returns the child adapter item with IME launch focus.
      */
     public AdapterItem getFocusedChild() {
+        if (mAdapterItems.size() == 0) {
+            return null;
+        }
         return mAdapterItems.get(getFocusedChildIndex());
     }