Added visual feedback for shader error

[williamchange]

suggestion via discord (by Arnklit)

Would it be possible to make the 2D preview show something else than the last succesfully rendered shader when you make a shader error?
like 😛

I just wish it did something else :P... it's just annoying when nothing is happening and you don't know it because it's still showing the last render. But yeah I didn't really think it was possible to catch this.

This uses get_shader_uniform_list().is_empty() to check if the shader compiles

error.mp4