char-lstm: invalid character index

When running the char-lstm example with no changes I occasionally get an error: `invalid character index`.

This is not a very big problem because after deleting any generated files (such as `vocab.dat`) everything works fine again. The real problem, however, is that when I change out the `input.txt` for my own file `language.txt` **(verified UTF-8)** it throws the same error (`invalid character index`) every time and will not work.

As mentioned I have verified that the text is indeed UTF-8 and is a *.txt file as should be. I have even gone so far as to remove all characters with accents to see if that could be the cause but still get the error.

I don't know if there is something I'm overlooking or if there is something that needs fixed here but it would be great to get it sorted out. I am running this on Ubuntu. Below is an example of text that my `language.txt` file contains:

> ENG: Why do we suffer?
> NAH: ¿Tleka titlajyouiyaj?
>
> ENG: How can we cope with life’s anxieties?
> NAH: ¿Kenon uelis tikxikoskej tlen techajmana?
>
> ENG: How can we make our family life happier?
> NAH: ¿Tlenon uelis tikchiuaskej tla tiknekij tinemiskej ika paktli iuan tochanejkauan?