Allow untokenized messages when using the prevent tokenization mode.

[ArEsKay3]

What does this PR do ?

Need to allow for the case that the incoming request doesn't have any previous tokenization metadata and just do tokenization normally even when "prevent_retokenization" is true.

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[santhnm2]

@ArEsKay3 This is different than the issue fixed in #3862 right?

[santhnm2]

LGTM but might be redundant with !3862, @i-riyad could you comment here?