Fix conversation accounts for migrated users

[akirk]

Summary

• When WP users were migrated to Friend terms, their post_author became 0 on existing conversation posts
• The Mastodon API conversation endpoint returned empty accounts arrays for these conversations
• This caused Tusky (and potentially other clients) to crash with IndexOutOfBoundsException when rendering conversations
• Fix: fall back to friends_feed_url post meta to resolve the account when post_author is 0

Test plan

• Check /api/v1/conversations returns non-empty accounts for all conversations
• Verify conversations from remote users (previously migrated) show the correct account

Changelog

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Type

• Fixed

Message

Fix conversation accounts for migrated users by falling back to friends_feed_url meta when post_author is 0.

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