ERROR in read_paf() with only one line in the PAF file

[lileiting]

Hi,

I found that if the PAF file has only one line, the read_paf() function will break with an error of Error in if (nrow(tag_mx_nr) == 0) { : argument is of length zero.

This was caused by this line

tag_mx_nr <- na.omit(unique(tag_mx[, 1:2]))

https://github.com/thackl/gggenomes/blob/daa8f87aa5080e88688b22db041f68ffb28f6fa5/R/read_paf.R#L78C33-L78C39

I suggest change it to

tag_mx_nr <- na.omit(unique(tag_mx[, 1:2, drop = FALSE]))

Thanks for developing the gggenomes package.

Leiting