Refactor migration

[VirginiaDooley]

This change reverts https://github.com/DemocracyClub/yournextrepresentative/pull/2424 and checks the queued_images is not None before filtering.

[sentry-io[bot]]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: ynr/apps/people/migrations/0047_alter_personimage_options_personimage_created_and_more.py

Function	Unhandled Issue
get_timestamp_from_queued_image	AttributeError: 'QueuedImage' object has no attribute 'modified' people.migrations.0047_alter_personimage_options_personimage_created_and_more in get_timestamp_f... Event Count: 6
get_timestamp_from_queued_image	AttributeError: 'NoneType' object has no attribute 'updated' people.migrations.0047_alter_personimage_options_personimage_created_and_more in get_timestampfrom... Event Count: 2

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