TASK: Close should check if the current socket is null

If we call close (by ex. during a reconnect) but the streamSocket is null, we generate useless error for the user.

Author: dfeyer

src/Nats/Connection.php

@@ -492,6 +492,9 @@ public function setChunkSize($chunkSize)
      */
     public function close()
     {
+        if ($this->streamSocket === null) {
+            return;
+        }
         fclose($this->streamSocket);
         $this->streamSocket = null;
     }