fix(client): don't spawn pool idle interval if timeout is 0 (#215)

Author: seanmonstar

src/client/legacy/pool.rs

@@ -426,6 +426,9 @@ impl<T: Poolable, K: Key> PoolInner<T, K> {
         } else {
             return;
         };
+        if dur == Duration::ZERO {
+            return;
+        }
         let timer = if let Some(timer) = self.timer.clone() {
             timer
         } else {