title: Shader: Mesh Renderer and Sprite Renderer are not respecting sorting order
body: <p>I have a fbx model that uses Unity's mobile unlit shader and another sprite that uses a custom shader. I have checked that they are both in the same renderer queue, however, they don't draw in respect of the sorting order but of the depth only.</p>
  <p>When I have sorting order of the sprite renderer set to 100 and sorting order of the mesh renderer set to 0, I'm expecting to see the sprite drawn in front of the model, regardless of the depth. But that's not what I am getting.</p>
  <p>Currently, the 3D model is using Unity's built-in mobile unlit shader (<a href="https://github.com/TwoTailsGames/Unity-Built-in-Shaders/blob/master/DefaultResourcesExtra/Mobile/Mobile-Lightmap-Unlit.shader" rel="nofollow noreferrer">https://github.com/TwoTailsGames/Unity-Built-in-Shaders/blob/master/DefaultResourcesExtra/Mobile/Mobile-Lightmap-Unlit.shader</a>),
  and my custom sprite shader has these flags set in a SubShader block:</p>
  <pre><code>    Lighting Off
      Cull Off
      ZWrite Off
      BlendOp [_OpColor]
      Blend [_SrcFactor] [_DstFactor]
  </code></pre>
  <p>Please let me know if there are ways to achieve this?</p>