Using ø in subject throws a waring in smpt_send

[alofting]

The problem is in the header_unstructured() function. sprintf seems to have an unnecessary parameter 0.

library(blastula)
blastula:::header_unstructured('ø' , "Subject", encode_unicode = TRUE)
#> Warning in sprintf("=?utf-8?B?%s?=", base64enc::base64encode(charToRaw(str)), :
#> one argument not used by format '=?utf-8?B?%s?='
#> [1] "=?utf-8?B?w7g=?="

^{Created on 2022-05-28 by the reprex package (v2.0.1)}