Don't unwrap client

If Smithay posts an error, client will become None immediately, even
while the surface may still receive events.

src/handlers/compositor.rs

@@ -59,8 +59,9 @@ impl CompositorHandler for State {
             });
             if let Some(dmabuf) = maybe_dmabuf {
                 if let Ok((blocker, source)) = dmabuf.generate_blocker(Interest::READ) {
-                    let client = surface.client().unwrap();
-                    let res = state
+                    if let Some(client) = surface.client() {
+                        let res =
+                            state
                                 .niri
                                 .event_loop
                                 .insert_source(source, move |_, _, state| {
@@ -75,6 +76,7 @@ impl CompositorHandler for State {
                         }
                     }
                 }
+            }
         });
     }