#338 Post-Python 3: Moderator queue fails for non-existent users

[Ahasuerus]

Post-Python 3: Moderator queue fails for non-existent users. As per https://isfdb.org/wiki/index.php/User:Alvonruff/Python3_Manual_Mod_List :

In determine_css_class(), after the self-approver, own-submission, and moderator checks all fail, the code accesses self.wiki_edits[submitter_id] without a guard. If get_wiki_edit_counts() did not return a record for this submitter (e.g. the submitter has never made a Wiki edit and no record exists), KeyError is raised, crashing the rendering pipeline before any table is displayed.

Note that this scenario is currently impossible because ISFDB users have to register on the Wiki side before they can create submissions. However, it would still be nice to fix the code to account for this scenario.