Fix connection null issue

if the connection isn't found in the connections. don't add it to the ready list.

Author: shtse8

lib/ConnectionPool.php

@@ -112,6 +112,9 @@ public function useExceptions($set) {
 
     private function ready($hash) {
         $conn = $this->connections[$this->connectionMap[$hash]];
+        if (!$conn) {
+            return;
+        }
         if (list($deferred, $method, $args) = $this->virtualConnection->getCall()) {
             $deferred->resolve(call_user_func_array([$conn, $method], $args));
         } else {