Don't crash trying to disable lockdown VPN

Bug: 28624328
Change-Id: I2b726453da43feaf5f46d45679a702a52e6f4df0
diff --git a/src/com/android/settings/vpn2/ConfigDialogFragment.java b/src/com/android/settings/vpn2/ConfigDialogFragment.java
index 0dbaa9a..788b9a9 100644
--- a/src/com/android/settings/vpn2/ConfigDialogFragment.java
+++ b/src/com/android/settings/vpn2/ConfigDialogFragment.java
@@ -176,6 +176,7 @@
         try {
             LegacyVpnInfo connected = mService.getLegacyVpnInfo(UserHandle.myUserId());
             if (connected != null && profile.key.equals(connected.key)) {
+                VpnUtils.clearLockdownVpn(getContext());
                 mService.prepareVpn(VpnConfig.LEGACY_VPN, VpnConfig.LEGACY_VPN,
                         UserHandle.myUserId());
             }