Fix Clipped Corners in NONE Background Mode

[TokisanGames]

When using the NONE background mode to cut off the mesh outside of regions, the +X, +Z corner and opposite look fine, but the -X,+Z corner and the opposite have clipped vertices.

If need be, this can be fixed by changing get_region_uv as follows.

ivec3 get_region_uv(const vec2 uv, const int search) {
    vec2 r_uv = uv;
    vec2 o_uv = mod(r_uv,_region_size);
    ivec2 pos;
    int bounds, layer_index = -1;
    for (int i = -1; i < clamp(search, SKIP_PASS, FRAGMENT_PASS); i++) {
        if ((layer_index == -1 && _background_mode == 0u ) || i < 0) {
            r_uv -= i == -1 ? vec2(0.0) : vec2(float(o_uv.x <= o_uv.y), float(o_uv.y <= o_uv.x));
            pos = ivec2(floor((r_uv) * _region_texel_size)) + (_region_map_size / 2);
            bounds = int(uint(pos.x | pos.y) < uint(_region_map_size));
            layer_index = (_region_map[ pos.y * _region_map_size + pos.x ] * bounds - 1);
        }
        
    }
    if (layer_index == -1) {
            r_uv = vec2(uv.x - float(search), uv.y);
            pos = ivec2(floor((r_uv) * _region_texel_size)) + (_region_map_size / 2);
            bounds = int(uint(pos.x | pos.y) < uint(_region_map_size));
            layer_index = (_region_map[ pos.y * _region_map_size + pos.x ] * bounds - 1);
    }
    if (layer_index == -1) {
            r_uv = vec2(uv.x, uv.y - float(search));
            pos = ivec2(floor((r_uv) * _region_texel_size)) + (_region_map_size / 2);
            bounds = int(uint(pos.x | pos.y) < uint(_region_map_size));
            layer_index = (_region_map[ pos.y * _region_map_size + pos.x ] * bounds - 1);
    }
    return ivec3(ivec2(mod(r_uv,_region_size)), layer_index);
}

We didn't think it was worth all of this code, so 2 clipped corners are the default.