`vec_order_base()` returns incorrect results with 0-col data frames

[DavisVaughan]

This is using CRAN vctrs, where we still called this vec_order(). Noticed here tidyverse/dplyr#6093 (comment)

library(vctrs)

df <- new_data_frame(n = 5L)

# Should return c(1, 2, 3, 4, 5)
vec_order(df)
#> NULL

^{Created on 2021-11-18 by the reprex package (v2.0.1)}

[DavisVaughan]

This in turn screws up vec_sort(), which I noticed while working on tidyr tidyverse/tidyr#1261

library(vctrs)

df <- new_data_frame(n = 5L)

vec_sort(df)
#> data frame with 0 columns and 0 rows

^{Created on 2021-12-13 by the reprex package (v2.0.1)}