AddDetail renders the bar even when OptionSetVisibility(false)

[tsuyukidev]

Fixes #236.

AddDetail calls render() when it records the first detail, without checking config.invisible. Every other render entry point checks it first (Add64, Describe, RenderBlank, renderDetails), so an invisible bar stays quiet right up until the first AddDetail, which then paints a line:

bar := progressbar.NewOptions64(100,
    progressbar.OptionSetVisibility(false),
    progressbar.OptionSetMaxDetailRow(2),
)
bar.Add(10)        // no output
bar.AddDetail("x") // renders a 0% bar

Guarding the initial render with !p.config.invisible matches the surrounding methods. renderDetails() already returns early when invisible, so the rest of the path was fine.