SocketApi: Fix crash with readyRead() after disconnected() #7044

SocketApi: Fix crash with readyRead() after disconnected() #7044

With the recent bugfix to avoid sending messages on dead connections
0bfe7ac250c54f5415c0a794c7b271428e83c3cf
the client now crashed if readyRead() was received after disconnected()
for the socket as the listener for that connection was already removed.

This code fixes it by still invoking the handler from readyRead() but
passing a SocketListener that won't attempt to send messages.