title: Can't create SDL2 texture using SDL_PIXELFORMAT_NV12 pixel format
body: <p>I'm using SDL 2.0.5 and Windows 10 to create a window and display a texture.</p>
  
  <p>Everything works fine when the texture has been initialized with SDL_PIXELFORMAT_YV12 pixel format, but when I set the format to SDL_PIXELFORMAT_NV12, SDL_CreateTexture function returns null. </p>
  
  <p>Here's the code:</p>
  
  <pre><code>SDL_Window* window = SDL_CreateWindow(
      "Test",
      SDL_WINDOWPOS_UNDEFINED,
      SDL_WINDOWPOS_UNDEFINED,
      width,
      height,
      SDL_WINDOW_FULLSCREEN_DESKTOP
  );
  
  SDL_Renderer* renderer = SDL_CreateRenderer(window , -1, SDL_RENDERER_SOFTWARE);
  
  SDL_Texture* texture = SDL_CreateTexture(
      renderer,
      SDL_PIXELFORMAT_NV12,
      SDL_TEXTUREACCESS_STREAMING,
      width,
      height
  );
  </code></pre>
  
  <p>Am I missing something?</p>