touchevents: set the screen pointer after checking the device is enabled

If the device is disabled the sprite is NULL so we get a seg fault
5 jobs for nacho/touch-events in 7 minutes and 8 seconds (queued for 3 seconds)
latest
Status Name Job ID Coverage
  Docker Image
passed debian-buster #13440978

00:01:00

 
  Build And Test
passed autotools #13440979

00:06:07

passed meson #13440980

00:02:24

passed meson-noglamor #13440981

00:01:55

passed mingw-cross-build #13440982

00:00:48