vnc: don't set the quality if lossy encoding are disabled This should not change the current behavior, but if any new encoding try to use the tight quality, it will always be set to -1 when lossy encodings are disabled. Signed-off-by: Corentin Chary <corentincj@iksaif.net> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>