setup_buffer() fails if global config.enabled is false

[brglng]

Problem

If the global config.enabled is false, setup_buffer() fails with an error.

Steps to reproduce

1. Use this global setup

require('ibl').setup {
    enabled = false,
}

2. Call :lua require("ibl").setup_buffer(0, {enabled = true}) on a buffer after Neovim is started.
3. See an error message attempt to index a nil value

Expected behavior

IBL should be enabled on the current buffer.

Neovim version (nvim -v)

0.9.2

[lukas-reineke]

Thanks, should be fixed now

[brglng]

Thanks!