Fixed ExtractCloakMeshBlueprint which assumes Categories being called on a unit without Categories.

[The-Balthazar]

[MrRowey]

@The-Balthazar can you please make sure that there is a description provided so I can be understood at a late date https://github.com/FAForever/fa/blob/develop/.github/pull_request_template.md As the template shows you also require the snippet. See https://github.com/FAForever/fa/blob/develop/changelog/snippets/fix.6342.md for how it is done

[lL1l1]

Reported on Discord.

Bug was in the original implementation of the extraction function.

Tested by removing the categories table from UEL0001 and making sure the blueprint loading phase passes successfully.