Fix wait condition and ordering in send().

precise/lib.go

@@ -138,12 +138,12 @@ func (s *state[T]) send(value T, buf *circ.B[T], cond *sync.Cond) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	for {
+		for !s.closed && !buf.CanPush() {
+			cond.Wait()
+		}
 		if s.closed {
 			panic("send on closed queue")
 		}
-		for !buf.CanPush() {
-			cond.Wait()
-		}
 		if buf.CanPush() {
 			buf.PushBack(value)
 			s.canRecv.Broadcast()