clients: add global_remove handler stubs

All the clients here were missing the global_remove handler. Because
window.c did not have it, weston-desktop-shell and weston-keyboard
segfaulted on compositor exit, as they received some
wl_registry.global_remove events.

Add more or less stub global_remove handlers, so that clients do not
crash on such events. Toytoolkit and all applications would need a lot
more code to properly handle the global object removal.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/clients/screenshot.c b/clients/screenshot.c
index 8681a41..efacfed 100644
--- a/clients/screenshot.c
+++ b/clients/screenshot.c
@@ -128,8 +128,15 @@
 	}
 }
 
+static void
+handle_global_remove(void *data, struct wl_registry *registry, uint32_t name)
+{
+	/* XXX: unimplemented */
+}
+
 static const struct wl_registry_listener registry_listener = {
-	handle_global
+	handle_global,
+	handle_global_remove
 };
 
 static struct wl_buffer *