当启动参数过长，访问/vars会导致dashboard崩溃

[Yinrong]

Describe the bug (描述bug)

当启动参数过长，访问/vars会导致dashboard崩溃
To Reproduce (复现方法)

启动参数超过1024个字节，然后使用/vars接口访问
Expected behavior (期望行为)

Versions (各种版本)
OS:
Compiler:
brpc:
protobuf:

Additional context/screenshots (更多上下文/截图)