DM preview shows JSON if the most recent message contains only an embed

[fluxbug-flutter]

Steps to reproduce

1. Receive a DM consisting of only an embed
2. Look at the preview

Expected behaviour

Preview should be empty/show some text content from the embed

Actual behaviour

JSON is shown instead

Client and system settings

Version 1.0.0, Beta 39, Channel Beta, Build 45, iOS 16.6 (arm64), Device iPhone10,3, Locale en-US, Push apns, Flutter 3.44.7, Dart 3.12.2

Stances

Approvals

• Acceptable & Valid on Beta 39, Build 45.

Denials

None

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Reported: #1280