Call reload_model_params only if there's no optimizer state
# What does this PR do ?

Checkpoint restoration process (roughly):
1. generate a state dict that contains model's state dict and optimizer's state dict.
2. load the two state dicts from the file checkpoint
3. restore model's state from the state contained in the checkpoint
4. reload optimizer params from the model's state.
5. restore optimizer's state from the state contained in the checkpoint.


The bug was in (1) and (4), the optimizer state does not contain cloned tensors but rather references. As a result, when the parameters were reloaded in (4) they were actually overwriting what was restored in (2) (in particular the fp32_from_fp16_params).

**Collection**: [Note which collection this PR will affect]

# Changelog 
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# Additional Information
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