fix: 修复aws claude渠道panic的问题

relay/channel/aws/relay-aws.go

@@ -222,9 +222,11 @@ func awsStreamHandler(c *gin.Context, resp *http.Response, info *relaycommon.Rel
 		}
 	}
 	service.Done(c)
+	if resp != nil {
 		err = resp.Body.Close()
 		if err != nil {
 			return service.OpenAIErrorWrapperLocal(err, "close_response_body_failed", http.StatusInternalServerError), nil
 		}
+	}
 	return nil, &usage
 }