GetVirtualMachinesMetricID method throwing panic error when accessing VMs from reponse

**Problem**: VirtualMachineService.GetVirtualMachinesMetricID method throws panic when it is trying to access the VMs response from server in below line of code. This happens when the count in the response is 1 but the actual VirtualMachinesMetrics array in the reponse is nil or empty. This is causing panic in the caller [CAPC](https://github.com/kubernetes-sigs/cluster-api-provider-cloudstack/blob/7b87895be9aa7d9dca1e2f70892feafd33ca4e59/pkg/cloud/instance.go#L61)

panic error is happening at: https://github.com/apache/cloudstack-go/blob/main/cloudstack/VirtualMachineService.go#L5543

**error**: `panic: runtime error: index out of range [0] with length 0`

version of cloudstack-go used: `2.16.1`

Please help investigate this error and let us know if this response is not expected

检查 CAPC 的 cloudstack/VirtualMachineService.go 第 5543 行，以及 pkg/cloud/instance.go 第 61 行的调用方。重现 count 为 1 但 VirtualMachinesMetrics 为 nil 或为空的响应，然后确定预期的处理方式，使该方法不再 panic，并通过文档或回归测试覆盖该响应行为。

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