AO3-4728 Fix Error 500 on subscriptions page for invalid items (#4816) #4432

Job	Run time
rake db:otwseed	1m 18s
rspec spec/controllers	11m 19s
rspec spec/models	5m 35s
rspec --exclude-pattern 'spec/{controllers,models}/*/.rb'	7m 30s
cucumber features/admins	5m 44s
cucumber features/bookmarks	4m 46s
cucumber features/collections	6m 2s
cucumber features/comments_and_kudos	8m 8s
cucumber features/gift_exchanges	6m 48s
cucumber features/importing	3m 1s
cucumber features/other_a	10m 33s
cucumber features/other_b	7m 32s
cucumber features/prompt_memes_a	4m 0s
cucumber features/prompt_memes_b	3m 54s
cucumber features/prompt_memes_c	4m 43s
cucumber features/search	6m 43s
cucumber features/tag_sets	3m 41s
cucumber features/tags_and_wrangling	7m 2s
cucumber features/users	5m 18s
cucumber features/works	13m 57s
	2h 7m 34s

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