sync: bounded channel can not have 0 size (#879)

tokio-sync/tests/mpsc.rs

@@ -65,6 +65,12 @@ fn send_recv_with_buffer() {
     assert!(val.is_none());
 }
 
+#[test]
+#[should_panic]
+fn buffer_gteq_one() {
+    mpsc::channel::<i32>(0);
+}
+
 #[test]
 fn send_recv_unbounded() {
     let (mut tx, mut rx) = mpsc::unbounded_channel::<i32>();