Fix tlayer torch JIT export

[WilliamTambellini]

Fix tlayer torch JIT export exception: "Could not cast value of type NoneType to bool" When torch jit exporting, self.need_attn is None. Fix #4459

Before submitting

• [ ] Was this discussed/approved via a Github issue? (no need for typos, doc improvements): Issue created 1 month ago, no comment.
• [X] Did you read the contributor guideline?
• [ ] Did you make sure to update the docs?
• [ ] Did you write any new necessary tests? I will if anyone comments/considers it necessary

What does this PR do?

Fixes #4459.

PR review

Anyone in the community is free to review the PR once the tests have passed. If we didn't discuss your PR in Github issues there's a high chance it will not be merged. I ve created the Github issue 1 month ago, no comment as today: #4459

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