gpui: Simplify tab group lookup logic in SystemWindowTabController (#40466)

Refactor the find_tab_group method to use the question mark operator for
cleaner error handling, replacing the explicit if-else pattern with a
more concise chained approach.

Release Notes:

- N/A

Signed-off-by: Xiaobo Liu <cppcoffee@gmail.com>

crates/gpui/src/app.rs

@@ -344,13 +344,9 @@ impl SystemWindowTabController {
         let tab_group = self
             .tab_groups
             .iter()
-            .find_map(|(group, tabs)| tabs.iter().find(|tab| tab.id == id).map(|_| *group));
+            .find_map(|(group, tabs)| tabs.iter().find(|tab| tab.id == id).map(|_| *group))?;
 
-        if let Some(tab_group) = tab_group {
-            self.tab_groups.get(&tab_group)
-        } else {
-            None
-        }
+        self.tab_groups.get(&tab_group)
     }
 
     /// Initialize the visibility of the system window tab controller.