Fix crash on invalid username in forums import

app/utils/__init__.py

@@ -19,11 +19,16 @@ import secrets
 from .flask import *
 from .models import *
 from .user import *
+import re
 
 
 YESES = ["yes", "true", "1", "on"]
 
 
+def is_username_valid(username):
+	return username is not None and len(username) >= 2 and re.match(r"^[A-Za-z0-9._-]*$", username)
+
+
 def isYes(val):
 	return val and val.lower() in YESES