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

Release Notes:

- N/A

crates/gpui/src/util.rs

@@ -1,3 +1,5 @@
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::SeqCst;
 #[cfg(any(test, feature = "test-support"))]
 use std::time::Duration;
 
@@ -108,3 +110,18 @@ impl std::fmt::Debug for CwdBacktrace<'_> {
         fmt.finish()
     }
 }
+
+/// Increment the given atomic counter if it is not zero.
+/// Return the new value of the counter.
+pub(crate) fn atomic_incr_if_not_zero(counter: &AtomicUsize) -> usize {
+    let mut loaded = counter.load(SeqCst);
+    loop {
+        if loaded == 0 {
+            return 0;
+        }
+        match counter.compare_exchange_weak(loaded, loaded + 1, SeqCst, SeqCst) {
+            Ok(x) => return x + 1,
+            Err(actual) => loaded = actual,
+        }
+    }
+}