memset zero _clients struct for server

fixes #244

src/WebSocketsServer.cpp

@@ -43,6 +43,8 @@ WebSocketsServer::WebSocketsServer(uint16_t port, String origin, String protocol
     _httpHeaderValidationFunc = NULL;
     _mandatoryHttpHeaders = NULL;
     _mandatoryHttpHeaderCount = 0;
+
+    memset(&_clients[0], 0x00, (sizeof(WSclient_t) * WEBSOCKETS_SERVER_CLIENT_MAX));
 }