Clear thumbnail/screenshot when forwarding media

Co-authored-by: Fedor Indutny <79877362+indutny-signal@users.noreply.github.com>

ts/util/maybeForwardMessages.preload.ts

@@ -148,6 +148,9 @@ export async function maybeForwardMessages(
           (attachments || []).map(async item => ({
             ...(await loadAttachmentData(item)),
             path: undefined,
+            thumbnail: undefined,
+            thumbnailFromBackup: undefined,
+            screenshot: undefined,
           }))
         );
         const attachmentsToSend = attachmentsWithData.filter(