Add default scales if not present before `new_scale()` about ggnewscale

[eliocamp]

Fixed :)

library(ggplot2)
library(ggnewscale)
topography <- expand.grid(x = 1:nrow(volcano),
                          y = 1:ncol(volcano))
topography$z <- c(volcano)

set.seed(42)
measurements <- data.frame(x = runif(30, 1, 80),
                           y = runif(30, 1, 60),
                           thing = rnorm(30))

ggplot(mapping = aes(x, y)) +
  geom_contour(data = topography, aes(z = z, color = stat(level))) +
  new_scale_color() +
  geom_point(data = measurements, size = 3, aes(color = thing)) +
  scale_color_viridis_c(option = "A")

^{Created on 2019-07-05 by the reprex package (v0.3.0)}