Fix bug in username validation function

[Mohamed-Elmanzalawi]

Expected Behavior

Should return False if the username starts with a non-ascii character

Actual Behavior

Returns True even if the username starts with a non-ascii character such as a period (.)

Steps to Reproduce the Problem

Add the following line at the end of the script: print(validate_user(".blue.kale", 3))
Run the script using python3 [script_name].py
Output: True