[BUG] offload optmizer states in zero3

[Hanqer]

Describe the bug
https://github.com/microsoft/DeepSpeed/blob/master/deepspeed/runtime/engine.py#L3736 In offloading states of zero3 engine, the assertion 'self.zero_offload_param()' return a config class but not bool, why check it as not?
'assert not self.zero_offload_param()' will always raise an error when the ds_config set as:

"offload_optimizer": {
"device": "none"
}

[tohtana]

Good catch, thank you @Hanqer!
As long as I check the behaviors of DeepSpeed engine, it returns None when offload_param is not given. We need to cover the case the device for offloading is none. The same goes for offloading of optimizer states.

I submitted #6855 to address this issue. I would appreciate it if you could give us any feedback.

[tohtana]

Closing as #6855 resolved this.