java.lang.IllegalArgumentException: Negative initial size: -1

Following error can be seen in the logs of the pulsar manager:

```
18:04:02.914 [pulsar-external-web-4-5] WARN org.eclipse.jetty.server.HttpChannel - /admin/v2/clusters
java.lang.IllegalArgumentException: Negative initial size: -1
at java.io.ByteArrayOutputStream.(ByteArrayOutputStream.java:74) ~[?:1.8.0_232]
at org.apache.pulsar.proxy.server.AdminProxyHandler$ReplayableProxyContentProvider.(AdminProxyHandler.java:150) ~[org.apache.pulsar-pulsar-proxy-2.4.2.jar:2.4.2]
```
It happens when the pulsar manager tries to communicate to the broker via the pulsar proxy. Proxy is working just fine when producing and consuming messages via python client code. The pulsar manager UI just spins.

Possibly similar issue to https://github.com/streamnative/pulsarctl/pull/157