fix(segmented-button): crash when context menu is unassigned

src/widget/segmented_button/widget.rs

@@ -883,6 +883,7 @@ where
                         }
 
                         // Present a context menu on a right click event.
+                        if self.context_menu.is_some() {
                             if let Some(on_context) = self.on_context.as_ref() {
                                 if right_button_released(&event)
                                     || (touch_lifted(&event) && fingers_pressed == 2)
@@ -903,6 +904,7 @@ where
                                 }
                             }
                         }
+                    }
 
                     break;
                 }