Handle panic on missing `search-paths`

[mkatychev]

The config below will panic on an .unwrap()

  openscad_lsp = {
    settings = {
      openscad = {
        fmt_style = "file",
        fmt_exe= "clang-format",
        -- search_paths = "/libs", this will panic if left commented
      },
    },
  }

modified unwrap to be unwrap_or_default