Server crash when sending message if user not found

[Jeelislive]

In server/index.js, getUser(socket.id) can return undefined (e.g., if a client emits sendMessage before completing join or after disconnect). Accessing user.room then throws and can crash the server.

Steps to reproduce

1. Connect a socket.
2. Do not emit join, or disconnect quickly after joining.
3. Emit sendMessage.

Expected behavior

• Server validates the sender; if user is missing, it returns an error to the client and does not crash.

Actual behavior

• Server attempts to access user.room and throws, potentially terminating the process.

Affected files

• server/index.js (handler socket.on('sendMessage', ...))