Fix bug: NullPointerException in ChooserActivity

Add a null check for mResolverDrawerLayout in ChooserActivity

Bug: 162900698
Test: ChooserActivityTest
Change-Id: Id2b4442a0c5f22e1ecff04a1d20b48784ecc47dd

core/java/com/android/internal/app/ChooserActivity.java

@@ -3134,7 +3134,9 @@ public class ChooserActivity extends ResolverActivity implements
         // ends up disabled. That's because at some point the old tab's vertical scrolling is
         // disabled and the new tab's is enabled. For context, see b/159997845
         setVerticalScrollEnabled(true);
-        mResolverDrawerLayout.scrollNestedScrollableChildBackToTop();
+        if (mResolverDrawerLayout != null) {
+            mResolverDrawerLayout.scrollNestedScrollableChildBackToTop();
+        }
     }
 
     @Override