UI: Fix unencoded stream failure

A stream will fail to start if the output_info does not have an
encoded_audio_codecs string, even if the output is not flagged as
encoded. This allows unencoded outputs to omit that string.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f