client: fix - exit on bad display-effect argument
client: fix - exit on bad display-effect argument

fgouget/spice,ya-mouse/spice,ya-mouse/spice,alon/spice-server,elmarco/spice,elmarco/spice,dezelin/spice,dezelin/spice,mathslinux/spice,mathslinux/spice,ya-mouse/spice,virtualAMP/spiceplay,virtualAMP/spiceplay,virtualAMP/spiceplay,mathslinux/spice,mathslinux/spice,alon/spice-server,alon/spice-server,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,mathslinux/spice,Fantu/spice,elmarco/spice,SPICE/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,Fantu/spice,dezelin/spice,dezelin/spice,Fantu/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,alon/spice-server,fgouget/spice,SPICE/spice,alon/spice-server,dezelin/spice,virtualAMP/spiceplay