ui/vnc: fix tight palette pixel encoding for 8/16-bpp formats

ui/vnc: fix tight palette pixel encoding for 8/16-bpp formats

When sending a tight rectangle with the palette filter, if the client
format was 8/16bpp, the colours on big endian hosts are not set as
we're sending the wrong bytes. We must first cast the 32-bit colour
to a 16/8-bit value, and then send the result.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit 63d320909220a90647c484263ae5e2f26eb54587)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>