WebGLRenderer: Release cache at the end of .render().

[takahirox]

I think it's better to release _currentCamera at the end of WebGLRenderer's .render(). Unless doing this, disposed camera resource won't be released until next .render() call because renderer keeps a reference to camera.

[mrdoob]

Say that we're rendering a scene with just one object and one material...
Wouldn't be doing unnecessary binding calls when rendering again?

[takahirox]

What does "binding calls" mean by in this context?

[takahirox]

Ah, binding buffer, isn't it?

Even in the current impl it binds every frame for a scene with one object and one material because it releases the cache at the beginning of .render(). So this PR change nothing about binding calls.

[Mugen87]

@mrdoob This PR is about when a cache or cache-like variables should be resetted.

Similar like the reset of render states and lists, the mentioned code block should be moved at the end of render(). In this way, the cache variables do no hold references to objects after the method has been quitted. This change does not increase the number of binding calls.

[mrdoob]

@Mugen87 Is it safe to merge?

[mrdoob]

I guess there is only one way to know... 🤓

[mrdoob]

Thanks!