Could subplot have explicit error when ncols is passed?

I just tried to use subplot in a shiny app, and naively assumed that there would be an ncols argument corresponding to nrows - evidently, that is not really needed, but an error message clearer than Error in [[: subscript out of bounds would have saved me a lot of confusion. Might still be worth making this explicit? (Or - though that might be too much of a change - require all ... arguments to be unnamed?)

library(plotly)
p1 <- plot_ly(economics, x = ~date, y = ~uempmed)
p2 <- plot_ly(economics, x = ~date, y = ~unemploy)
subplot(p1, p2, ncols = 2)
#> Error in plots[[i]][["frames"]]: subscript out of bounds

^{Created on 2024-05-09 with reprex v2.0.2}

首先，在 subplot 的入口点重现所提供的 R 示例，并检查 ncols 参数的处理方式。完成的标准是，传入 ncols 不再产生 subscript-out-of-bounds 错误，而是给出清晰且有意设计的消息；检查结果时，请考虑 issue 中所描述的 subplot 现有行为。