Handle users being deleted in getUserHandle.

getUserHandle by serial number calls getUserInfoLocked
which may return null for a user that exists when its
being deleted.

Change-Id: I949831f8bc959e5ec1f3cb907d86313f10e12554
diff --git a/services/core/java/com/android/server/pm/UserManagerService.java b/services/core/java/com/android/server/pm/UserManagerService.java
index f85b195..07584b3 100644
--- a/services/core/java/com/android/server/pm/UserManagerService.java
+++ b/services/core/java/com/android/server/pm/UserManagerService.java
@@ -1786,7 +1786,8 @@
     public int getUserHandle(int userSerialNumber) {
         synchronized (mPackagesLock) {
             for (int userId : mUserIds) {
-                if (getUserInfoLocked(userId).serialNumber == userSerialNumber) return userId;
+                UserInfo info = getUserInfoLocked(userId);
+                if (info != null && info.serialNumber == userSerialNumber) return userId;
             }
             // Not found
             return -1;