Limit sender username

Reviewed-on: Kelder/cammiechat#7

chat.py

@@ -105,6 +105,8 @@ def messages_post():
         if "X-Username" in request.headers and len(request.headers["X-Username"]) > 0:
             sender = request.headers["X-Username"]
             sendertype = "name"
+            if len(sender) > 50:
+                return "Username too long"
         elif "X-Real-IP" in request.headers:
             sender = reverse_lookup(request.headers["X-Real-IP"])
             sendertype = "ip"