Fix bug removing all windows that belong to a display.

Removing one window causes its subwindows to also be removed.
We have to be careful when traversing the window list
because multiple windows may be removed at a time so we
don't get IndexOutOfBoundsException due to the window
list changing in unexpected ways.

Bug: 7273702
Change-Id: I0ed9ba00c325ad178ab28919ce2e763cb6fd38ba

Author: Jeff Brown

services/java/com/android/server/wm/WindowManagerService.java

@@ -10870,8 +10870,8 @@ private void handleDisplayRemovedLocked(int displayId) {
         final DisplayContent displayContent = getDisplayContentLocked(displayId);
         mDisplayContents.delete(displayId);
         WindowList windows = displayContent.getWindowList();
-        for (int i = windows.size() - 1; i >= 0; --i) {
-            final WindowState win = windows.get(i);
+        while (!windows.isEmpty()) {
+            final WindowState win = windows.get(windows.size() - 1);
             removeWindowLocked(win.mSession, win);
         }
         mAnimator.removeDisplayLocked(displayId);