[Panic] When the mq server is unavailable, calling the SendAsync interface will panic

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**BUG REPORT**
1. Please describe the issue you observed:

- What did you do (The steps to reproduce)?
When the mq server is unavailable, calling the SendAsync interface will panic，

- What did you expect to see?
The rocketmq go client captures exceptions and uses the function return value err to represent the execution result.

- What did you see instead?
time="2024-09-28T11:18:13+08:00" level=error msg="get consumer list of group from broker error" broker="10.129.21.242:10911" consumerGroup=xxxxxxxxxxxxxxxxxxxxx underlayError="request timeout"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xbc295e]

goroutine 738949296 [running]:
github.com/apache/rocketmq-client-go/v2/internal.(*rmqClient).ProcessSendResponse(0x0?, {0xc004939140?, 0xffffffffffffffff?}, 0x0, 0xc0001d7110?, {0xc01f46a258?, 0x1?, 0x1?})
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/client.go:730 +0x3e
github.com/apache/rocketmq-client-go/v2/producer.(*defaultProducer).sendAsync.func1(0xc00f69b980?, {0x1bd4000, 0xc0001d7110})
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/producer/producer.go:411 +0x128
github.com/apache/rocketmq-client-go/v2/internal.(*rmqClient).InvokeAsync.func1(0x0?)
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/client.go:591 +0x2b
github.com/apache/rocketmq-client-go/v2/internal/remote.(*ResponseFuture).executeInvokeCallback.func1()
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/remote/future.go:50 +0x2a
sync.(*Once).doSlow(0xc01f0095c0?, 0x0?)
/usr/local/go/src/sync/once.go:68 +0xc2
sync.(*Once).Do(...)
/usr/local/go/src/sync/once.go:59
github.com/apache/rocketmq-client-go/v2/internal/remote.(*ResponseFuture).executeInvokeCallback(0xc0212265f0?)
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/remote/future.go:48 +0x45
github.com/apache/rocketmq-client-go/v2/internal/remote.(*remotingClient).receiveAsync(0xc01cd4ffb8?, 0x92ae5f?)
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/remote/remote_client.go:139 +0x34
github.com/apache/rocketmq-client-go/v2/internal/remote.(*remotingClient).InvokeAsync.func1()
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/remote/remote_client.go:129 +0x2f
github.com/apache/rocketmq-client-go/v2/primitive.WithRecover(0xc019ef5620?)
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/primitive/base.go:100 +0x3e
created by github.com/apache/rocketmq-client-go/v2/internal/remote.(*remotingClient).InvokeAsync
/root/go/pkg/mod/github.com/apache/rocketmq-client-go/v2@v2.1.2/internal/remote/remote_client.go:128 +0x20c

2. Please tell us about your environment:

- What is your OS?
Centos

- What is your client version?
github.com/apache/rocketmq-client-go/v2 v2.1.2

- What is your RocketMQ version?
4.3.0