constructing unt sq with ignore_case = TRUE doesn't ignore case enough

[ErdaradunGaztea]

Describe the bug
Using alphabet = "unt" with ignore_case = TRUE does not ignore case completely, instead, ignores case for those lowercase letters, that appear as uppercase as well. If no uppercase equivalent is present, letter is treated as NA.

To Reproduce

# simply run
sq(c("oXYOqwwKCNJLo"), alphabet = "unt", ignore_case = TRUE)

Expected behavior
Above call should return sq object of type unt with all letters as uppercase, with no NA, that is, !.