fix(miiorobot): Fix ERR_HTTP_HEADERS_SENT exception

[004helix]

Type of change

Type A:

• Bug fix (non-breaking change which fixes an issue)
• UI Feature
• Refactor/Code Cleanup
• Docs
• Capability implementation for existing core capability
• New robot implementation

Description (Type A)

Fix unhandled exception on miio_client start/restart

[2022-05-12T21:31:35.232Z] [ERROR] Unhandled WebServer Error Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at new NodeError (node:internal/errors:377:5)
    at ServerResponse.setHeader (node:_http_outgoing:576:11)
    at ServerResponse.header (/snapshot/Valetudo/node_modules/express/lib/response.js:776:10)
    at ServerResponse.send (/snapshot/Valetudo/node_modules/express/lib/response.js:170:12)
    at ServerResponse.json (/snapshot/Valetudo/node_modules/express/lib/response.js:267:15)
    at ServerResponse.send (/snapshot/Valetudo/node_modules/express/lib/response.js:158:21)
    at /snapshot/Valetudo/backend/lib/robots/MiioValetudoRobot.js:304:29
    at Layer.handle [as handle_request] (/snapshot/Valetudo/node_modules/express/lib/router/layer.js:95:5)
    at next (/snapshot/Valetudo/node_modules/express/lib/router/route.js:137:13)
    at Route.dispatch (/snapshot/Valetudo/node_modules/express/lib/router/route.js:112:3) {
  code: 'ERR_HTTP_HEADERS_SENT'
}