Render queue of this material.
By default materials use render queue of the shader it uses. You can override
the render queue used using this variable. Note that once render queue is set on the material,
it stays at that value, even if shader is later changed to be different.
Render queue number should be positive to work properly; or -1 to use the render queue from the shader.
See Also: Shader.renderQueue, RenderQueue tag.