Fix binding of texture()

[davepagurek]

Resolves #7665

Changes

Previously, we fixed a bug where a texture bound to a shader would unbind after its first use. So, textures stay bound. This lead to a scenario where if you draw using a framebuffer as a texture once:

texture(myFramebuffer)

...then if you later try to draw to that framebuffer, even without a texture applied, it would cause a feedback cycle since the framebuffer is still bound to the shader:

myFramebuffer.draw(() => {
  lights()
  circle(0, 0, 20) // Logs an error, doesn't draw anything in firefox
})

The problem is that we were using texture() to bind a texture, but when no texture is applied (e.g. after a pop()), we we're unbinding.

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated