treemap should not creates viewport if draw = FALSE

[mcanouil]

Thanks for developing this R package!

Currently treemap::treemap opens a new grid viewport by default and does not respect draw = FALSE.
If draw = FALSE, no graphics device should be open.

To cleanly embed treemap() function into other code/function, you have to make ugly things like the code below which is not ideal.

library(treemap)
data(GNI2014)

grDevices::pdf(file = "/dev/null")
treemap(
  dtf = GNI2014,
  index = c("continent", "iso3"),
  vSize = "population",
  vColor = "GNI",
  type = "value",
  format.legend = list(scientific = FALSE, big.mark = " "),
  draw = FALSE
)
invisible(grDevices::dev.off())

For short, all viewports functions should be conditional on draw.