Fix possible crash in the onTaskRemoved() method of LinphoneService if the LinphoneManager has already been destroyed.

src/android/org/linphone/LinphoneManager.java

@@ -487,7 +487,7 @@ public class LinphoneManager implements LinphoneCoreListener, LinphoneChatMessag
 
 		if (sExited) {
 			throw new RuntimeException("Linphone Manager was already destroyed. "
-					+ "Better use getLcIfManagerNotDestroyed and check returned value");
+					+ "Better use getLcIfManagerNotDestroyedOrNull and check returned value");
 		}
 
 		throw new RuntimeException("Linphone Manager should be created before accessed");

src/android/org/linphone/LinphoneService.java

@@ -801,7 +801,8 @@ public final class LinphoneService extends Service {
 
 			// If push is enabled, don't unregister account, otherwise do unregister
 			if (LinphonePreferences.instance().isPushNotificationEnabled()) {
-				LinphoneManager.getLc().setNetworkReachable(false);
+				LinphoneCore lc = LinphoneManager.getLcIfManagerNotDestroyedOrNull();
+				if (lc != null) lc.setNetworkReachable(false);
 			}
 			stopSelf();
 		}