`footnote(threeparttable=TRUE)` does not work with multiple footnotes

[vincentarelbundock]

kableExtra::footnote inserts multiple nested threeparttable environments when calling the function multiple times. This prevents LaTeX from compiling:

library(kableExtra)
kbl(head(mtcars), "latex") %>%
    footnote(general = "First note",
             general_title = "",
             threeparttable = TRUE) %>%
    footnote(general = "Second note",
             general_title = "",
             threeparttable = TRUE)

#> 
#> \begin{threeparttable}
#> \begin{threeparttable}
#> \begin{tabular}[t]{l|r|r|r|r|r|r|r|r|r|r|r}
#> \hline
#>   & mpg & cyl & disp & hp & drat & wt & qsec & vs & am & gear & carb\\
#> \hline
#> Mazda RX4 & 21.0 & 6 & 160 & 110 & 3.90 & 2.620 & 16.46 & 0 & 1 & 4 & 4\\
#> \hline
#> Mazda RX4 Wag & 21.0 & 6 & 160 & 110 & 3.90 & 2.875 & 17.02 & 0 & 1 & 4 & 4\\
#> \hline
#> Datsun 710 & 22.8 & 4 & 108 & 93 & 3.85 & 2.320 & 18.61 & 1 & 1 & 4 & 1\\
#> \hline
#> Hornet 4 Drive & 21.4 & 6 & 258 & 110 & 3.08 & 3.215 & 19.44 & 1 & 0 & 3 & 1\\
#> \hline
#> Hornet Sportabout & 18.7 & 8 & 360 & 175 & 3.15 & 3.440 & 17.02 & 0 & 0 & 3 & 2\\
#> \hline
#> Valiant & 18.1 & 6 & 225 & 105 & 2.76 & 3.460 & 20.22 & 1 & 0 & 3 & 1\\
#> \hline
#> \end{tabular}
#> \begin{tablenotes}
#> \item Second note
#> \end{tablenotes}
#> \end{threeparttable}
#> \begin{tablenotes}
#> \item First note
#> \end{tablenotes}
#> \end{threeparttable}