gpui: Fix race condition when upgrading a weak reference (#30952)

Release Notes:

- N/A

crates/gpui/src/window.rs

@@ -52,6 +52,7 @@ use uuid::Uuid;
 
 mod prompts;
 
+use crate::util::atomic_incr_if_not_zero;
 pub use prompts::*;
 
 pub(crate) const DEFAULT_WINDOW_SIZE: Size<Pixels> = size(px(1024.), px(700.));
@@ -263,15 +264,13 @@ impl FocusHandle {
     pub(crate) fn for_id(id: FocusId, handles: &Arc<FocusMap>) -> Option<Self> {
         let lock = handles.read();
         let ref_count = lock.get(id)?;
-        if ref_count.load(SeqCst) == 0 {
-            None
-        } else {
-            ref_count.fetch_add(1, SeqCst);
-            Some(Self {
-                id,
-                handles: handles.clone(),
-            })
+        if atomic_incr_if_not_zero(ref_count) == 0 {
+            return None;
         }
+        Some(Self {
+            id,
+            handles: handles.clone(),
+        })
     }
 
     /// Converts this focus handle into a weak variant, which does not prevent it from being released.