ui: remove unreachable code in vnc_update_client

A previous commit:

  commit 5a8be0f73d6f60ff08746377eb09ca459f39deab
  Author: Gerd Hoffmann <kraxel@redhat.com>
  Date:   Wed Jul 13 12:21:20 2016 +0200

    vnc: make sure we finish disconnect

Added a check for vs->disconnecting at the very start of the
vnc_update_client method. This means that the very next "if"
statement check for !vs->disconnecting always evaluates true,
and is thus redundant. This in turn means the vs->disconnecting
check at the very end of the method never evaluates true, and
is thus unreachable code.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20171218191228.31018-3-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
