title: onNext() onError() callbacks not executing on second subscribtion android
body: <p>I've an Observable something like this:</p>
  
  <pre><code>@GET("endpoint")
  Observable&lt;Something&gt; getSomething();
  </code></pre>
  
  <p>and Subscriber like this </p>
  
  <pre><code>Subscriber&lt;Something&gt; somethingSubscriber = new Subscriber&lt;Something&gt;() {
          public void onCompleted() {
      }
  
          public void onError(Throwable e) {
          //handle exceptions
      }
  
          public void onNext() {
          //do something
      }
  </code></pre>
  
  <p>In my OnClickListener associated with a button, i make a subscription</p>
  
  <pre><code>getSomething()
       .subscribeOn(Schedulers.newThread())
       .observeOn(AndroidSchedulers.mainThread())
       .subscribe(somethingSubscriber);
  </code></pre>
  
  <p>If i don't have an internet connection, onError is called and i do some exception handling. when I press the button again (assume i want to retry), the callback methods do not get called.</p>
  
  <p>I want that onNext / onError callbacks get called everytime I press the button.</p>