Fix 找不到$client的BUG (swoft-cloud/swoft-component#199)

Author: limingxinleo

src/Service.php

@@ -109,7 +109,9 @@ public function call(string $func, array $params)
             $result = $packer->unpack($result);
             $data   = $packer->checkData($result);
         } catch (\Throwable $throwable) {
-            $client && $client->close();
+            if (isset($client) && $client instanceof AbstractServiceConnection) {
+                $client->close();
+            }
             if (empty($fallback)) {
                 throw $throwable;
             }