hue_pal with direction= -1 seems broken

[bbarthold]

After switching from grDevices::hcl to farver::encode_colour, negative hues generated in hue_pal function when setting direction to -1 do not seem to work as expected.

See results from running show_col(hue_pal(direction = -1)(9)) using scales v.1.1.0 (farver 2.0.3) below

library(scales)
show_col(hue_pal(direction = -1)(9))

sessionInfo()
#> R version 3.6.2 (2019-12-12)
#> Platform: x86_64-pc-linux-gnu (64-bit)
#> Running under: Ubuntu 19.10
#> 
#> Matrix products: default
#> BLAS:   /usr/lib/x86_64-linux-gnu/openblas/libblas.so.3
#> LAPACK: /usr/lib/x86_64-linux-gnu/libopenblasp-r0.3.7.so
#> 
#> locale:
#>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
#>  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
#>  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
#>  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
#>  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
#> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] scales_1.1.0
#> 
#> loaded via a namespace (and not attached):
#>  [1] Rcpp_1.0.3       digest_0.6.23    R6_2.4.1         lifecycle_0.1.0 
#>  [5] magrittr_1.5     evaluate_0.14    highr_0.8        rlang_0.4.4     
#>  [9] stringi_1.4.5    farver_2.0.3     rmarkdown_2.1    tools_3.6.2     
#> [13] stringr_1.4.0    munsell_0.5.0    xfun_0.12        yaml_2.2.1      
#> [17] compiler_3.6.2   colorspace_1.4-1 htmltools_0.4.0  knitr_1.27

^{Created on 2020-02-04 by the reprex package (v0.3.0)}