the additional arguments (e.g., offset, scale) in `add.gdsn()` have no effect when `val=NULL`

[zhengxwen]

library(gdsfmt)

packageVersion("gdsfmt")

f <- createfn.gds("test.gds")
n <- add.gdsn(f, "new", val=NULL, storage="packedreal16", offset=1, scale=0.1)
print(n, attribute=TRUE)

Output:

[1] ‘1.5.12’

+ new   { PackedReal16 0, 0 byte }< [offset: 0; scale: 1e-04] 

offset should be 1 and scale should be 0.1.