attachment lost when replying

[tomholub]

to reproduce:

1. receive an encrypted message
2. reply all
3. attach a file (tested with 6mb image)
4. add body and send

expected result: sent reply contains the attachment

actual result: attachment missing

works on new messages

[tomholub]

observed on #1420

[DenBond7]

I can reproduce that. But I'm not sure that it was caused by #1420.