Fix NPE when view a single photo.

bug: 6995776
Change-Id: Iba213dfefcab04f2c856f55dc3446e3314f30a6f
diff --git a/src/com/android/gallery3d/actionbar/SystemActionBarWrapper.java b/src/com/android/gallery3d/actionbar/SystemActionBarWrapper.java
index 3c4dac5..2d70aa6 100644
--- a/src/com/android/gallery3d/actionbar/SystemActionBarWrapper.java
+++ b/src/com/android/gallery3d/actionbar/SystemActionBarWrapper.java
@@ -169,18 +169,21 @@
 
     @Override
     public void setMenuItemVisible(int menuItemId, boolean visible) {
+        if (mMenu == null) return;
         MenuItem item = mMenu.findItem(menuItemId);
         if (item != null) item.setVisible(visible);
     }
 
     @Override
     public void setMenuItemTitle(int menuItemId, String title) {
+        if (mMenu == null) return;
         MenuItem item = mMenu.findItem(menuItemId);
         if (item != null) item.setTitle(title);
     }
 
     @Override
     public void setMenuItemIntent(int menuItemId, Intent intent) {
+        if (mMenu == null) return;
         MenuItem item = mMenu.findItem(menuItemId);
         if (item != null) item.setIntent(intent);
     }