Show full message in Saved Messages displays epoch 0 timestamp

- Summary: When expanding a very long text message in Saved Messages by clicking “show full message”, the displayed timestamp changes to epoch 0 (1970-01-01 or similar) instead of the correct message time. The timestamp remains correct when the message is collapsed, and in the chat list. - Operating System (Linux/Mac/Windows/iOS/Android): Mac - Delta Chat Version: v2.48.0 - Expected behavior: The timestamp should remain unchanged and display the correct message time, whether collapsed or expanded. - Actual behavior: After expanding, the timestamp incorrectly changes to epoch 0. Collapsing restores the correct time. - Steps to reproduce the problem: 1. Open DeltaChat and go to Saved Messages (chat with yourself). 2. Send a very long text message (long enough to be truncated with a “show full message” button). 3. Observe the timestamp - it shows the correct sent time initially. 4. Tap/click “show full message” to expand the entire text. 5. Look at the timestamp again - it now shows epoch 0 (e.g., Thursday, January 1, 1970 [timezone] AM). - Screenshots: <img width="1036" height="303" alt="Image" src="https://github.com/user-attachments/assets/7b1c8cab-f98d-4263-9dad-3b4228f9d2b6" /> - Logs: - Additional Observations 1. Timestamp is correct in chat list view. 2. Timestamp is correct in message info/details panel. 3. Bug occurs only in Saved Messages (not in chats with other contacts). 4. Bug occurs only while expanded; collapsing fixes it.