screen-share: clear dirty flag after output update

Clear the dirty flag after the output has been updated. This reduces
background CPU load noticably when screen share is active from ~1% to
0% on my laptop. Tested with screen-share RDP backend, no negative
impact observed.

Fixes: 47928d87 ("Add a screen sharing plugin")
Signed-off-by: Stefan Agner <stefan@agner.ch>
2 jobs for clear-dirty-flag in 1 minute and 6 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Container Prep
passed #371401
container_prep

00:00:21

 
  Build
passed #371402
build-native-meson

00:00:45