Avoids error in case there's no more servers logged in but the app was caught...

Avoids error in case there's no more servers logged in but the app was caught in the middle of connection retry

app/src/main/java/chat/rocket/android/service/RocketChatWebSocketThread.java

@@ -255,6 +255,10 @@ public class RocketChatWebSocketThread extends HandlerThread {
     return prepareDDPClient()
         .flatMap(_val -> Single.fromEmitter(emitter -> {
           ServerInfo info = connectivityManager.getServerInfoForHost(hostname);
+          if (info == null) {
+            emitter.onSuccess(false);
+            return;
+          }
           RCLog.d("DDPClient#connect");
           ddpClient.connect(info.getSession(), info.isSecure())
               .onSuccessTask(task -> {