[gnome-shell] dash: Fix some JS warnings

[Florian Müllner <fmuellner src gnome org>]

commit 2a01606c59894b366ff9fbbeb7cadda2d5c70dc8
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Jun 13 03:41:42 2017 +0200

    dash: Fix some JS warnings
    
    We currently use "array[index]" to test whether an array has an
    element at index before using it. However nowadays gjs warns about
    accessing non-existent array elements, so the test itself already
    produces a warning. Avoid this by checking the array length before
    using an index to access an element.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=781471

 js/ui/dash.js |   26 ++++++++++++++------------
 1 files changed, 14 insertions(+), 12 deletions(-)
---
diff --git a/js/ui/dash.js b/js/ui/dash.js
index 802ae53..2252a74 100644
--- a/js/ui/dash.js
+++ b/js/ui/dash.js
@@ -756,42 +756,44 @@ const Dash = new Lang.Class({
         let newIndex = 0;
         let oldIndex = 0;
         while (newIndex < newApps.length || oldIndex < oldApps.length) {
+            let oldApp = oldApps.length > oldIndex ? oldApps[oldIndex] : null;
+            let newApp = newApps.length > newIndex ? newApps[newIndex] : null;
+
             // No change at oldIndex/newIndex
-            if (oldApps[oldIndex] == newApps[newIndex]) {
+            if (oldApp == newApp) {
                 oldIndex++;
                 newIndex++;
                 continue;
             }
 
             // App removed at oldIndex
-            if (oldApps[oldIndex] &&
-                newApps.indexOf(oldApps[oldIndex]) == -1) {
+            if (oldApp && newApps.indexOf(oldApp) == -1) {
                 removedActors.push(children[oldIndex]);
                 oldIndex++;
                 continue;
             }
 
             // App added at newIndex
-            if (newApps[newIndex] &&
-                oldApps.indexOf(newApps[newIndex]) == -1) {
-                addedItems.push({ app: newApps[newIndex],
-                                  item: this._createAppItem(newApps[newIndex]),
+            if (newApp && oldApps.indexOf(newApp) == -1) {
+                addedItems.push({ app: newApp,
+                                  item: this._createAppItem(newApp),
                                   pos: newIndex });
                 newIndex++;
                 continue;
             }
 
             // App moved
-            let insertHere = newApps[newIndex + 1] &&
-                             newApps[newIndex + 1] == oldApps[oldIndex];
+            let nextApp = newApps.length > newIndex + 1 ? newApps[newIndex + 1]
+                                                        : null;
+            let insertHere = nextApp && nextApp == oldApp;
             let alreadyRemoved = removedActors.reduce(function(result, actor) {
                 let removedApp = actor.child._delegate.app;
-                return result || removedApp == newApps[newIndex];
+                return result || removedApp == newApp;
             }, false);
 
             if (insertHere || alreadyRemoved) {
-                let newItem = this._createAppItem(newApps[newIndex]);
-                addedItems.push({ app: newApps[newIndex],
+                let newItem = this._createAppItem(newApp);
+                addedItems.push({ app: newApp,
                                   item: newItem,
                                   pos: newIndex + removedActors.length });
                 newIndex++;