[R/update_cell_loop] further speedups

[JanMarvin]

Well, sometimes it's the little things, like writing correct c++-code.

> library(microbenchmark)
> library(openxlsx2)
> 
> # a larger data frame with strings, missings and numbers
> xlsxFile <- system.file("extdata", "readTest.xlsx", package = "openxlsx2")
> wb1 <- wb_load(xlsxFile)
> data <- wb_to_df(wb1, sheet = 3, skipEmptyRows = TRUE)
> 
> res <- microbenchmark::microbenchmark(
+   wb <- wb_workbook()$add_worksheet()$add_data(x = data),
+   wb <- wb$add_data(x = data),
+   times = 25
+ ); res
Unit: milliseconds
                                                   expr       min        lq     mean    median        uq       max neval
 wb <- wb_workbook()$add_worksheet()$add_data(x = data)  31.77736  32.08635  34.6002  32.37475  32.69734  44.95653    25
                            wb <- wb$add_data(x = data) 143.69455 145.38906 149.5828 146.44222 155.83526 161.53349    25

25s -> 145ms. I'm calling it a day. Only 4.3 times slower :)

[Edit:] previously the initial creation was part of my speed measurement 🙈