Describe the bug
Changing nickname in a groupchat once forbids to change nickname in another groupchat afterward.

To Reproduce
I connect anonymously to a groupchat foo@example.com with the nickname Alice. I change my nickname to Bob. Then, I create a new groupchat on the same server (using the + button), for example bar@example.com. I appear there as Alice (which is expected, because the "Nickname" button says it is to change our nickname in the current groupchat). The issue is then when I try to change my nickname in bar@example.com, it actually changes it in foo@example.com. So, I'm stuck with the Alice nickname on bar@example.com.

Expected behavior
The nickname button should change the nickname in the current visible groupchat.

Environment (please complete the following information):

• Desktop
• Browser Firefox
• Converse.js version 10.1.7