VNC/RFB: QEMU reports incorrect name (length)

If the name of a machine (as set with the -name argument) has a length longer than 1024, (RFB) VNC clients will not receive a correct RFB ServerInit message.

I suspect this is the problem:

https://github.com/qemu/qemu/blob/master/ui/vnc.c#L2463

The return value of snprintf is used as the value for the name-length field in the ServerInit message.
This is problematic for names that were truncated to 1024, as the length will now be bigger than the actual name.

I think a quick fix would be to simply report min(size,1024) to the client...