Merge "Prevent potential NPE when forcing stop package during boot"

services/core/java/com/android/server/wm/ActivityTaskManagerService.java

@@ -6099,7 +6099,8 @@ public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
         public boolean onForceStopPackage(String packageName, boolean doit, boolean evenPersistent,
                 int userId) {
             synchronized (mGlobalLock) {
-
+                // In case if setWindowManager hasn't been called yet when booting.
+                if (mRootWindowContainer == null) return false;
                 return mRootWindowContainer.finishDisabledPackageActivities(packageName,
                         null /* filterByClasses */, doit, evenPersistent, userId,
                         // Only remove the activities without process because the activities with