clients/fullscreen: Refuse to resize the surface size when fullscreen'ed

This would be causing a protocol error in which the buffer size needs to
match the one provided in the configure event.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
2 jobs for fix-xdg-ack in 1 minute and 37 seconds (queued for 15 seconds)
latest
Status Job ID Name Coverage
  Container Prep
passed #535718
container_prep

00:00:31

 
  Build
passed #535719
build-native-meson

00:01:05