Force single stack id workaround. (Bug 19560619)

Change-Id: Ia3cbe0ca75b018bf499a814f37d8a532d52981f1
diff --git a/packages/SystemUI/src/com/android/systemui/recents/model/RecentsTaskLoadPlan.java b/packages/SystemUI/src/com/android/systemui/recents/model/RecentsTaskLoadPlan.java
index 788e473..5d98dda 100644
--- a/packages/SystemUI/src/com/android/systemui/recents/model/RecentsTaskLoadPlan.java
+++ b/packages/SystemUI/src/com/android/systemui/recents/model/RecentsTaskLoadPlan.java
@@ -156,6 +156,7 @@
 
             if (!mConfig.multiStackEnabled ||
                     Constants.DebugFlags.App.EnableMultiStackToSingleStack) {
+                firstStackId = 0;
                 ArrayList<Task> stackTasks = stacksTasks.get(firstStackId);
                 if (stackTasks == null) {
                     stackTasks = new ArrayList<Task>();