Fullscreen effect passes don't actually need a camera but WebGLRenderer.render requires one.

Use camera far of 1000 to support the claims in the comments.

This eliminates far scene blending artifacts (tiny dots in the middle of bright discs).

Scaled CoC values may be greater than 1.0 and can't be stored in buffers that use UnsignedByteType. This change makes CoC scaling more robust at the cost of an additional texel fetch in the DoF blend shader.