return mail content size as restore size (#3705)

#### Does this PR need a docs update or release note?

- [x] ⛔ No

#### Type of change

- [x] 🐛 Bugfix

#### Test Plan

- [x] ⚡ Unit test
- [x] 💚 E2E

src/internal/m365/exchange/mail_restore.go

@@ -159,7 +159,14 @@ func restoreMail(
 		return nil, clues.Stack(err)
 	}
 
-	return api.MailInfo(msg, int64(len(body))), nil
+	var size int64
+
+	if msg.GetBody() != nil {
+		bc := ptr.Val(msg.GetBody().GetContent())
+		size = int64(len(bc))
+	}
+
+	return api.MailInfo(msg, size), nil
 }
 
 func setMessageSVEPs(msg models.Messageable) models.Messageable {