`formatter_glue_or_sprintf`: error if `msg` is of length zero

[deeenes]

If the first argument for the log_* functions is a zero length vector the following error happens:

library(logger)
log_formatter(formatter_glue_or_sprintf)
log_success(character(0))
Error in regmatches(msg, gregexpr("%[0-9.+0]*[aAdifeEgGosxX]", msg))[[1]] : 
  subscript out of bounds

From here: https://github.com/daroczig/logger/blob/e88153b49678227f693115d0ca19c73cf87e355a/R/formatters.R#L83

I think this can happen easily in an unpredictable way, so would be nice to handle without error. Because there is no message, for logger the best would be to output nothing (or maybe one empty line).

[daroczig]

thanks for the report :+1: