This is something of a hack over the underlying problem of #1042 - we declare that a TextSeq contains only int, float, bytes but in no way do we check this. At least we will check it at the point where we actually call something that depends on it being bytes and only bytes.

Fixes: #1059

Tested by finding a PDF in samples/contrib with an identity CMap and putting a name object in the place of a string.

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