Using other than scalars for `gpar` does not work

[gvegayon]

The way I wrote set_gpar, it will replicate arguments and turn them into a list. Unfortunately, when passing an argument that IS A LIST, like grid::radialGradient(), does not work. This should be an easy fix.This is the code that fails:

p <- nplot(...)
p <- set_vertex_gpar(p, "core", fill = radialGradient(c("white", "black"), cx1=.8, cy1=.8, r1=0))
print(p) # fails