title: LibGDX actor doesn't show
body: <p>I have a problem with buttons and labels. 
  I have following code in Create method:</p>
  
  <pre><code>    Gdx.gl.glClearColor(1, 1, 1, 1);
      Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
  
  
      stage = new Stage(new ScreenViewport());
      atlas = new TextureAtlas("buttons/btnplay.pack");
      font = new BitmapFont();
  
      skin = new Skin(atlas);
  
      Table table = new Table(skin);
      table.setBounds(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
  
      TextButtonStyle style = new TextButtonStyle();
      style.up = skin.getDrawable("btndown");
      style.down = skin.getDrawable("btndown");
      style.font = font;
  
      TextButton btnPlay = new TextButton("DELAASDASDSAD",style);
      btnPlay.setPosition(100, 100);
      btnPlay.setWidth(100);
      btnPlay.setHeight(100);
  
      btnPlay.background(skin.getDrawable("btnup"));
  
      table.add(btnPlay);
  
      stage.addActor(btnPlay);
  </code></pre>
  
  <p>And in rendering method:</p>
  
  <pre><code>stage.act(Gdx.graphics.getDeltaTime());
  stage.draw();
  </code></pre>
  
  <p>Now the problem is that button or label doesn't show on screen and i don't see reason why.
  Any suggestion? </p>