fix: download entries CSV crashes with IndexError when round has no entries

[lgelauff]

Bug

download_round_entries_csv raises an unhandled IndexError when the round has no entries, producing a raw internal server error page instead of a meaningful message.

Traceback

IndexError: list index out of range
montage/admin_endpoints.py, line 294
csv_fieldnames = sorted(entry_infos[0].keys())

When it happens

Any attempt to download the entries CSV for a round that has no entries — for example:

• Round 1 before images have been imported
• A round where all entries were disqualified

Root cause

download_round_entries_csv derives CSV field names from the first element of entry_infos. If the list is empty, entry_infos[0] crashes. There is no guard for this case.

Fix

Add an early return before line 114 in admin_endpoints.py:

if not entry_infos:
    raise InvalidAction('no entries in round, cannot export CSV')

Confirmed on

montage-beta

[Sanika123-art]

I was able to reproduce this issue locally and confirmed that it occurs when attempting to download the entries CSV for a round with no entries.

I implemented a fix in PR #535 by adding a guard to handle the empty entry_infos list and return a proper error instead of causing an IndexError.

I also noticed that PR #532 addresses the same issue. Happy to update or close my PR if needed.