web3sdk 2.6.2 通过sdk.key sdk.crt加载时报错sslContext为空，改用node.key node.crt又成功了

sdk加载节点的sdk证书的默认文件名以前支持sdk.key和node.key，但是最近出现只有sdk.key文件名时启动失败

Reproduce the web3sdk 2.6.2 startup using sdk.key and sdk.crt, then compare it with the successful node.key and node.crt case. Trace the SDK certificate-file loading and SSL context initialization, and consider the issue done when the sdk.key/sdk.crt naming case starts successfully with a non-empty SSL context.

Written by the indexing model from the issue text.