Fixes #1873537.

Only update the popup window when it is shown. This avoids throwing an NPE in PopupWindow.
A PopupWindow is only aware of its content view after being shown.

core/java/android/widget/AbsListView.java

@@ -1570,7 +1570,7 @@ public abstract class AbsListView extends AdapterView<ListAdapter> implements Te
         if (mInstallGesturesOverlay) {
             installGesturesOverlay();
             positionGesturesPopup();
-        } else if (mGesturesPopup != null) {
+        } else if (mGesturesPopup != null && mGesturesPopup.isShowing()) {
             mGesturesPopup.update(w, h);
         }
     }