android: Show an error if VPN fails due to lock down mode in Android 4.2

src/frontends/android/res/values-de/strings.xml

@@ -25,6 +25,7 @@
     <string name="search">Suchen</string>
     <string name="vpn_not_supported_title">VPN nicht unterstützt</string>
     <string name="vpn_not_supported">Ihr Gerät unterstützt keine VPN Anwendungen.\nBitte kontaktieren Sie den Hersteller.</string>
+    <string name="vpn_not_supported_during_lockdown">VPN Verbindungen sind nicht möglich im abgeriegelten Modus.</string>
     <string name="loading">Laden&#8230;</string>
 
     <!-- Log view -->

src/frontends/android/res/values-pl/strings.xml

@@ -27,6 +27,7 @@
     <string name="search">Szukaj</string>
     <string name="vpn_not_supported_title">Nie obsługiwany VPN</string>
     <string name="vpn_not_supported">Urządzenie nie obsługuje aplikacji VPN.\nProszę skontaktować się z producentem.</string>
+    <string name="vpn_not_supported_during_lockdown">Polączenia nie sa możliwe w trybie zamkniętym</string>
     <string name="loading">Wczytywanie&#8230;</string>
 
     <!-- Log view -->

src/frontends/android/res/values/strings.xml

@@ -25,6 +25,7 @@
     <string name="search">Search</string>
     <string name="vpn_not_supported_title">VPN not supported</string>
     <string name="vpn_not_supported">Your device does not support VPN applications.\nPlease contact the manufacturer.</string>
+    <string name="vpn_not_supported_during_lockdown">VPN connections are not supported in lockdown mode.</string>
     <string name="loading">Loading&#8230;</string>
 
     <!-- Log view -->

src/frontends/android/src/org/strongswan/android/ui/MainActivity.java

@@ -95,7 +95,17 @@ public class MainActivity extends Activity implements OnVpnProfileSelectedListen
 	 */
 	protected void prepareVpnService(Bundle profileInfo)
 	{
-		Intent intent = VpnService.prepare(this);
+		Intent intent;
+		try
+		{
+			intent = VpnService.prepare(this);
+		}
+		catch (IllegalStateException ex)
+		{
+			/* this happens if the always-on VPN feature (Android 4.2+) is activated */
+			VpnNotSupportedError.showWithMessage(this, R.string.vpn_not_supported_during_lockdown);
+			return;
+		}
 		/* store profile info until the user grants us permission */
 		mProfileInfo = profileInfo;
 		if (intent != null)