remove expect from fallible code, would crash if handling this outsid…

…e of winit

src/platform_impl/web/web_sys/canvas/pointer_handler.rs

@@ -79,9 +79,7 @@ impl PointerHandler {
                     event::mouse_button(&event),
                     event::mouse_modifiers(&event),
                 );
-                canvas
-                    .set_pointer_capture(event.pointer_id())
-                    .expect("Failed to set pointer capture");
+                let _e = canvas.set_pointer_capture(event.pointer_id());
             },
         ));
     }