Stream stuck loading if the page is refreshed while it loads

[Alexis Janon]

On the Anbox Cloud Dashboard version 1.21, refreshing the stream page while it's loading will make it stuck for a while before it errors out.

Steps to reproduce:
1. Access a session page at /sessions/<id>
2. Wait for the stream to appear
3. Refresh in the browser
4. Once the page is loaded, but while the stream itself still appears loading, refresh.

Then, the stream appears to be loading until we hit a timeout 5 minutes later, with the error message:

Anbox stream failed
signaling timed out