Fix index changed when no image in the directory in gallery

ui/file_manager/gallery/js/slide_mode.js

Index: ui/file_manager/gallery/js/slide_mode.js
diff --git a/ui/file_manager/gallery/js/slide_mode.js b/ui/file_manager/gallery/js/slide_mode.js
index 54ccfc190836c795c1f1bde488583cff4d7f9a5f..cd96aab6f52372df0e5aa444d8db56698f883be2 100644
--- a/ui/file_manager/gallery/js/slide_mode.js
+++ b/ui/file_manager/gallery/js/slide_mode.js
@@ -927,6 +927,9 @@ SlideMode.prototype.getNextSelectedIndex_ = function(direction) {
  * @param {string} keyID Key of the KeyboardEvent.
  */
 SlideMode.prototype.advanceWithKeyboard = function(keyID) {
+  if (this.selectionModel_.selectedIndex === -1)

[fukino, 2016/08/10 04:39:46]

What we want to do is "If there is no item, do not change the selectedIndex."
So, could you check the item's count instead of selectedIndex?

It is possible that selectedIndex is -1 but there are some items.

[harukam1, 2016/08/10 05:04:11]

Acknowledged.

+    return;
+
   var prev = (keyID === 'ArrowUp' ||
               keyID === 'ArrowLeft' ||
               keyID === 'MediaTrackPrevious');