ui: avoid pointless VNC updates if framebuffer isn't dirty

The vnc_update_client() method checks the 'has_dirty' flag to see if there are
dirty regions that are pending to send to the client. Regardless of this flag,
if a forced update is requested, updates must be sent. For unknown reasons
though, the code also tries to sent updates if audio capture is enabled. This
makes no sense as audio capture state does not impact framebuffer contents, so
this check is removed.

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: 20171218191228.31018-5-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
