Fix chameleon's TypeError because inputs_embeds may None
Author: YenFuLin
Pull request: yes

# What does this PR do?

When training Chameleon, I got the error message: "TypeError 'nonetype' object is not subscriptable". Because `inputs_embeds` may be None, I think it should check `inputs_embeds` type first before using it.

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Comments:
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cool, let's merge then!