Skip lockdown setup if user is not up yet

Sometimes USER_UNLOCKED can be sent before USER_STARTED. This puts
lockdown in a bad state as it needs a fully-functioning user to tie
itself to and listen for connectivity events.

Bug: 27637943
Change-Id: I41a784a75a8c8674cb61dbba10693dd56c9396dd

services/core/java/com/android/server/ConnectivityService.java

@@ -3253,8 +3253,12 @@ public class ConnectivityService extends IConnectivityManager.Stub
             }
             int user = UserHandle.getUserId(Binder.getCallingUid());
             synchronized(mVpns) {
-                setLockdownTracker(new LockdownVpnTracker(mContext, mNetd, this, mVpns.get(user),
-                            profile));
+                Vpn vpn = mVpns.get(user);
+                if (vpn == null) {
+                    Slog.w(TAG, "VPN for user " + user + " not ready yet. Skipping lockdown");
+                    return false;
+                }
+                setLockdownTracker(new LockdownVpnTracker(mContext, mNetd, this, vpn, profile));
             }
         } else {
             setLockdownTracker(null);