This patch checks that ioc is not null before
using it in tcp socket tcp_chr_add_watch function.

The failure occurs in replay mode of the execution,
when monitor and serial port are tcp servers,
and there are no clients connected to them:

-monitor tcp:127.0.0.1:8081,server,nowait
-serial tcp:127.0.0.1:8082,server,nowait

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <161284977034.741841.12565530923825663110.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>