Exporting all articles - metadata field issue

[S-Haime]

Describe the bug There is an issue with the metadata fields, where a field has been deleted but the answer is still stored. This causes an error when trying to do an export, making it impossible to export metadata. If the answer was stored so that it contains the question itself, rather than the linked object this might resolve the issue. Additionally, this shouldn't be killing the export even if an answer is not found.

Janeway version The version of Janeway under which the bug has been reproduced. If running off of master, please, indicate the current HEAD of the Janeway installation

To Reproduce Steps to reproduce the behavior:

1. https://jcls.io/plugins/imports/articles/all/
2. Export all or Export CSV.

Additional context Reported by jcls (ULB) FD 8101