compositor: check viewport dst size validity
compositor: check viewport dst size validity

wp_viewporter requires the destination size to be always in integers,
even when it is implicit from source rectangle. Emit appropriate
protocol errors.

Signed-off-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>
Reviewed-by: Bryce Harrington <bdb14cfc1ab8d24e13de84adc40b41ae60c13bd1@osg.samsung.com>

krezovic/weston,sir-murray/weston,sir-murray/weston,krezovic/weston