add-user.sh duplicates user records in "mgmt-users.properties" file if special character is used in user name

Description of problem:
add-user.sh duplicates user records in "mgmt-users.properties" file if special character is used in user name.

How reproducible:
Always

Steps to Reproduce:

1. cd ${JBOSS_HOME}/bin
2. ./add-user.sh -u "ádmin" -p Pes1234* -s
3. ./add-user.sh -u "admín" -p Pes1234* -s
4. ./add-user.sh -u "user1" -p Pes1234* -s
5. ./add-user.sh -u "user2" -p Pes1234* -s
6. cat ../standalone/configuration/mgmt-users.properties

Actual results:

...
ádmin=add08a6a96a2470830558e37e7cf5894
admín=6702e36900191d0a5438075e9298c950
ádmin=add08a6a96a2470830558e37e7cf5894
admín=6702e36900191d0a5438075e9298c950
ádmin=add08a6a96a2470830558e37e7cf5894
user1=f111b15c70bc1db3637e0b1dc6848b74
admín=6702e36900191d0a5438075e9298c950
user2=6671636ed99ff984187cd70a159df9af
ádmin=add08a6a96a2470830558e37e7cf5894
...