In R, how to prevent blank page in pdf when using gridBase to embed subplot inside plot

As explained here, it is easy to embed a plot into an existing one thanks to gridBase, even though both plots use the base graphics system of R. However, when saving the whole figure into a pdf, the first page is always blank. How to prevent this?

Here is an example:

require(gridBase)

## generate dummy data
set.seed(1859)
x <- 1:100
y <- x + rnorm(100, sd=5)
ols <- lm(y ~ x)

pdf("test.pdf")

## draw the first plot
plot.new() # blank page also happens when using grid.newpage()
pushViewport(viewport())
plot(x, y)

## draw the second plot, embedded into the first one
pushViewport(viewport(x=.75,y=.35,width=.2,height=.2,just=c("center","center")))
par(plt=gridPLT(), new=TRUE)
hist(ols$residuals, main="", xlab="", ylab="")
popViewport(2)

dev.off()