Correct out of range error in getTopVisibleActivities.

Looks like just a typo.

Test: Launch Settings > Google > Search > Voice > "OK Google" Detection. Train voice model. Say ok google.
Bug: 35590598
Change-Id: I882f5695a94940d0dc7df911b1f8d55e372d1828
diff --git a/services/core/java/com/android/server/am/ActivityStackSupervisor.java b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
index f49ad82..1c5233e 100644
--- a/services/core/java/com/android/server/am/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
@@ -4922,7 +4922,7 @@
     List<IBinder> getTopVisibleActivities() {
         final ArrayList<IBinder> topActivityTokens = new ArrayList<>();
         // Traverse all displays.
-        for (int i = mActivityDisplays.size(); i >= 0; i--) {
+        for (int i = mActivityDisplays.size() - 1; i >= 0; i--) {
             final ActivityDisplay display = mActivityDisplays.valueAt(i);
             // Traverse all stacks on a display.
             for (int j = display.mStacks.size() - 1; j >= 0; j--) {