title: SpriteKit animateWithTextures not work with texture atlas
body: <p>When I don't use texture atlas,everything works fine.But when I use texture atlas,animateWithTextures doesn't work and nothing appears.
  Here is my code</p>
  
  <pre><code>SKTexture *spaceshipTexture = [SKTexture textureWithImageNamed:@"monkey.png"];
  SKSpriteNode *spaceship = [SKSpriteNode spriteNodeWithTexture:spaceshipTexture];
  spaceship.position = CGPointMake(0,0);
  spaceship.anchorPoint = CGPointMake(0,0);
  [self addChild: spaceship];
  
  NSMutableArray *images=[NSMutableArray arrayWithCapacity:14];
  for (int i=1; i&lt;=14; i++) {
      NSString *fileName=[NSString stringWithFormat:@"%dShuGuangx.png",i];
      SKTexture *tempTexture=[SKTexture textureWithImageNamed:fileName];
      [images addObject:tempTexture];
  }
  NSLog(@"count %d",images.count);
  SKAction *walkAnimation = [SKAction animateWithTextures:images timePerFrame:0.1];
  [spaceship runAction:walkAnimation];
  </code></pre>