Preview fails to load when sending second message with attachments

After sending a message with an attachment, I'm unable to send a second message with an attachment because the preview fails to load.

Test device: Honor 8A (Android 9).

changed milestone to %Android 1.3

added Sponsor 1 ~2 labels

The bug doesn't exist on my attachment-refactoring branch, which also fixes an issue with unsent attachments not always being deleted. But since we're pushed for time I'll look for a small fix and save the refactoring for later.

mentioned in merge request !1144 (merged)

closed via merge request !1144 (merged)

mentioned in commit 5beed1a7