🐛 Fix bug in guide_circles() with multiple layers

[teunbrand]

This PR aims to fix #58.

The issue was that the layer-rejection mechanism of GuideLegend wasn't used properly.

devtools::load_all("~/packages/legendry/")
#> ℹ Loading legendry
#> Loading required package: ggplot2

ggplot(mtcars) +
  aes(x = mpg, y = hp, color = cyl) +
  geom_point(aes(x = mpg, y = hp, fill = cyl, size=hp), shape=21) +
  geom_smooth(aes(x = mpg, y = hp), inherit.aes = FALSE) +
  scale_size(breaks = c(100, 250), guide = "circles")
#> `geom_smooth()` using method = 'loess' and formula = 'y ~ x'

^{Created on 2025-02-17 with reprex v2.1.1}