clients/simple-egl: Exit when display has an error

Check return values for wl_display_dispatch_* functions, so that
the program stops running when the compositor that it is connected
to crashes.

Signed-off-by: Manuel Stoeckl <code@mstoeckl.com>
2 jobs for fix-exit in 1 minute and 27 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container Prep
passed #498489
container_prep

00:00:27

 
  Build
passed #498490
build-native-meson

00:01:00