Fix bug

Bug:  username must be edited in order to submit the form

Author: yuxuanleong

Frontend/src/components/user/EditProfile.jsx

@@ -51,7 +51,7 @@ function EditProfile() {
         const usernameRegex = /^[a-zA-Z0-9._]{3,20}$/;
         const isValidUsername = usernameRegex.test(username)
 
-        if(!isValidUsername) {
+        if(!isValidUsername && username !== "") {
             console.log("username is not valid:", username)
             setUsernameError(true)
             setErrorMessage("Username can only contain letters, numbers, dots (.), and underscores (_), and must be between 3 and 20 characters long.")