Patchwork crashes when combining plots with empty facet rows and/or columns

[ltuijnder]

Thanks for the amazing package! I really like it but I have encountered a bug the other day.
Below I give you a minimal example:

---

Combining figures that have an empty facet row results in a crash.

One can create a facet with an empty row using the ggforce::facet_wrap_paginate function. As shown in the minimal example below:

library(ggplot2)
library(ggforce)
library(patchwork)

out <- ggplot(diamonds) +
  geom_point(aes(carat, price), alpha = 0.1) +
  facet_wrap_paginate(~ cut:clarity, ncol = 3, nrow = 3, page = 5)

out # page 5 has an empty row

out + out 
#> Error in grid.Call.graphics(C_setviewport, vp, TRUE): invalid 'layout.pos.row'

^{Created on 2021-08-23 by the reprex package (v2.0.1)}

Package versions:
ggforce_0.3.3 patchwork_1.1.1 ggplot2_3.3.5

---

Other pages with fully or partially filled rows do not crash.

[ltuijnder]

After playing around I encountered an even more minimal example just using patchwork and ggplot2:

library(patchwork)
library(ggplot2)

p1 <- ggplot(mtcars) + 
  geom_point(aes(mpg, disp)) + 
  ggtitle('Plot 1')

patch <- wrap_plots(p1, nrow = 2) # empty second row
patch + patch
#> Error in grid.Call.graphics(C_setviewport, vp, TRUE): invalid 'layout.pos.row'

^{Created on 2021-08-24 by the reprex package (v2.0.1)}

Evidently, in this example I could have made better checks on the number of rows. Or if I want to go for a similar look I should use the patchwork::plot_spacer() function.

However, I do not have these luxuries when I use ggforce::facet_wrap_paginate and thus the problem persists.

[ltuijnder]

It also crashes with empty columns in a very similar fashion:

library(patchwork)
library(ggplot2)
p1 <- ggplot(mtcars) + geom_point(aes(mpg, disp))

emptyCol <- wrap_plots(p1, ncol = 2)
emptyCol + emptyCol
#> Error in grid.Call.graphics(C_setviewport, vp, TRUE): invalid 'layout.pos.col'

^{Created on 2021-08-31 by the reprex package (v2.0.1)}