The script uses
for u in $(cat $userslist); do
(echo -n "[*] user $u%$password " && rpcclient -U "$domain/$u%$password" -c "getusername;quit" $target) >> logs/spray-logs.txt
done
Without modifying IFS as so (this might be an improper fix though, as far as I'm concerned, the actual way to read lines in bash is with read, as in the password reading part of the script):
This translates into usernames with whitespace in them not being supported. the logs also use "cut -d ' ' ", that would also break with whitespace in the username