Fix exception on loading File Manager.

File manager updated commands availablility before roots loaded. Handling code exxpects a nonempty list that cause an exception.

BUG=None.
TEST=Check DevTools log.


Review URL: http://codereview.chromium.org/9705058

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@126920 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/file_manager/js/file_manager.js

@@ -1152,8 +1152,8 @@ FileManager.prototype = {
         var entry =
             this.getRootEntry_(this.rootsList_.selectionModel.selectedIndex);
 
-        return DirectoryModel.getRootType(entry.fullPath) ==
-               DirectoryModel.RootType.REMOVABLE;
+        return entry && DirectoryModel.getRootType(entry.fullPath) ==
+                        DirectoryModel.RootType.REMOVABLE;
     }
   };