Fix for Survery detailexport (#37733)

[mdezi]

excel detail export didnt function when trying to export surverys containing freetext answers - tried to access an array without checking wether the array key is set.

[kergomard]

Thank you very much @mdezi for the PR!

I labeled it as 'improvement' as there is no Mantis-Issue for it, but it looks rather like a 'bugfix'. Please see our guidelines for PRs here: https://github.com/ILIAS-eLearning/ILIAS/blob/trunk/docs/development/contributing.md#rules-for-contributors

Thanks again and best, @kergomard

[alex40724]

@mdezi Thanks for the PR. Could you please provide a bug report according to the mentioned guidelines. Thanks.

[mdezi]

I had commented my changes in this ticket ( https://mantis.ilias.de/view.php?id=37733 ) as it describes a similar case with the same issue. Shall i make a new ticket for it instead?

[alex40724]

Thanks, this should be fixed in the meantime.