Fix NPE in PreparePageFadeoutTexture

Bug: 8837688
Change-Id: Ie8fbd9a42497195b8a01cc5638cb0c44d4532d09
diff --git a/src/com/android/gallery3d/ui/PreparePageFadeoutTexture.java b/src/com/android/gallery3d/ui/PreparePageFadeoutTexture.java
index f52aa5f..ce672f2 100644
--- a/src/com/android/gallery3d/ui/PreparePageFadeoutTexture.java
+++ b/src/com/android/gallery3d/ui/PreparePageFadeoutTexture.java
@@ -17,6 +17,10 @@
     private GLView mRootPane;
 
     public PreparePageFadeoutTexture(GLView rootPane) {
+        if (rootPane == null) {
+            mCancelled = true;
+            return;
+        }
         int w = rootPane.getWidth();
         int h = rootPane.getHeight();
         if (w == 0 || h == 0) {