Fix the crash when home button is pressed.

When the fragment is going to be removed, we should ignore the events
left in the message queue.

bug:3392087
Change-Id: Ie716c9cc6742e9990c08d1428f10a956a727d6ed

src/com/android/settings/vpn/VpnSettings.java

@@ -688,7 +688,7 @@ public class VpnSettings extends SettingsPreferenceFragment
     }
 
     private void startVpnTypeSelection() {
-        if (getActivity() == null) return;
+        if ((getActivity() == null) || isRemoving()) return;
 
         ((PreferenceActivity) getActivity()).startPreferencePanel(
                 VpnTypeSelection.class.getCanonicalName(), null, R.string.vpn_type_title, null,
@@ -743,7 +743,7 @@ public class VpnSettings extends SettingsPreferenceFragment
     }
 
     private void startVpnEditor(final VpnProfile profile, boolean add) {
-        if (getActivity() == null) return;
+        if ((getActivity() == null) || isRemoving()) return;
 
         Bundle args = new Bundle();
         args.putParcelable(KEY_VPN_PROFILE, profile);