stat_density_2d in ggplot2: bandwidths must be strictly positive

Question

I'm trying to plot kernel density estimates for my data, but I'm getting an error ("bandwidths must be strictly positive") because the 0.25 and 0.75 quantiles are the same. A solution for this in MASS::kde2d was presented here, but I'm unsure how to write a function for h in stat_density_2d() that would work similarly.

The solution for kde2d is:

kde2d(df$s1x, df$s1y,
      h = c(ifelse(bandwidth.nrd(df$s1x) == 0, 0.1, bandwidth.nrd(df$s1x)),
            ifelse(bandwidth.nrd(df$s1y) == 0, 0.1, bandwidth.nrd(df$s1y))))

Because I'm faceting the plot, I need "h" to take a function that will work dynamically with facets or else I would add static values to "h".

Update: I've tried

h = c(function(x) ifelse(bandwidth.nrd(x)==0,0.01,bandwidth.nrd(x)),
      function(y) ifelse(bandwidth.nrd(y)==0,0.01,bandwidth.nrd(y)))

and

h= function(x) ifelse(x==c(0,0),c(0.01,0.01),x)

as well as a few variations, but without knowing exactly what's happening under the hood, I'm unsure how to code the function.

Here is some data I generated that may help:

xx <- rbind(data.frame(x = c(rep(30.00000,40),rep(30.00000,10)+rnorm(10)),
                 y = c(rep(-90.00000,40),rep(-90.00000,10)+rnorm(10)),
                 grp = 'A'),
            data.frame(x = c(rep(30.00000,50)+rnorm(50)),
                       y = c(rep(-90.00000,50)+rnorm(50)),
                       grp = 'B'))
ggplot()+
  stat_density_2d(data = xx, aes(x,y, fill = ..level..), geom = 'polygon')+
  facet_wrap(~grp)