Skip TTS events entirely with empty text

[synesthesiam]

Breaking change

Proposed change

When running a pipeline, TTS events were not supposed to be generated if the TTS input was empty. This PR skips the events, rather than just skipping the TTS generation.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
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Additional information

• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @balloob, mind taking a look at this pull request as it has been labeled with an integration (assist_pipeline) you are listed as a code owner for? Thanks!

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