"GL_INVALID_OPERATION: Array object is not active" when rendering bufferless quad

[heinezen]

Description

OpenGL generates an error when a bufferless quad is drawn but no VAO is bound. This can happen in the renderer here (line 57):

openage/libopenage/renderer/opengl/geometry.cpp

Lines 56 to 58 in 29df8ac

	case geometry_t::bufferless_quad:
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
	break;

Even though glDrawArrays doesn't read from a buffer, it requires a VAO as stated in the OpenGL Wiki:

A non-zero Vertex Array Object must be bound (though no arrays have to be enabled, so it can be a freshly-created vertex array object).

How To Reproduce

1. Create a GlGeometry object with a bufferless quad, e.g. with renderer::opengl::GlRenderer::add_bufferless_quad()
2. Create a renderable with the geometry
3. Add the renderable to a render pass
4. Render the render pass and observe the error

Expected Behavior

An empty VAO should be created and bound when trying to render a bufferless quad.