Method setOnError

src/main/java/field/graphics/Shader.java:239–242

(iErrorHandler onError)

		GL20.glDeleteProgram(s.name);
		// doesn't kill the shaders, because, technically they could be attached elsewhere
	}

	public Shader setOnError(iErrorHandler onError) {
		this.onError = onError;
		return this;
	}