Slice doesn't drop excess rows

[hadley]

Moved from tidyverse/dplyr#1446, by @franknarf1

library(dplyr, warn.conflicts = FALSE)
library(dtplyr)

df <- data.frame(x = c("a","a","b"), y = c(2,3,4))

tbl_df(df) %>% slice(3:4)
#> # A tibble: 1 x 2
#>   x         y
#>   <fct> <dbl>
#> 1 b         4
tbl_dt(df) %>% slice(3:4)
#> Source: local data table [2 x 2]
#> 
#> # A tibble: 2 x 2
#>   x         y
#>   <fct> <dbl>
#> 1 b         4
#> 2 <NA>     NA

^{Created on 2019-05-25 by the reprex package (v0.2.1.9000)}

[hadley]

Includes handling NA in indices