Override default fzfx window settings

[damanis]

I use the following code to change window split to horizontal.
It worked before but in last versions using it causes problem: it is impossible to use -- to specify additional rg arguments. What is not correct in this configuration code?

  local fzfx = require("fzfx")

  fzfx.setup({
    live_grep = {
        fzf_opts = {
          { "--prompt",         "Buffers > " },
          { "--delimiter",      ":" },
          { "--preview-window", "top,50%,+{2}-/2" },
        },
        win_opts = {
          height = 50,
          width = 0.9,
          row = -2,
        },
    },
  })

[linrongbin16]

Let's continue this issue here: #710.