Fix StableDiffusionPipeline when text_encoder=None

[DN6]

What does this PR do?

FIx for SD Pipeline when text_encoder=None and tokenizer=None

Fixes # (issue)
#8287

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[sayakpaul]

Thanks.

We should consider adding tests for this. I think this is a real scenario.

[sayakpaul]

Cc: @bghira could you test if this solves the issue you reported?

[yiyixuxu]

thanks!

[DN6]

We should consider adding tests for this. I think this is a real scenario.
@sayakpaul a fast test has been included in the PR.

[sayakpaul]

Thanks!