Fix sending message with attachments

[EgorovEI]

What was solved?
This PR fixes the case when OutgoingMessage stored in messagesSection did not include attachment object after sending. It led to the situation when the attachment was missed if initial send message request failed.
Now failed-to-send messages with attachments can be successfully resent.

Release notes:

• Feature
• Ignore
• Release notes (Is it clear from the description here?)
• Migration guide (If changes are needed for integrator already using the SDK - what needs to be communicated? Add underneath please)

Additional info:

• Is the feature sufficiently tested? All tests fixed? Necessary unit, acceptance, snapshots added? Check that at least new public classes & methods are covered with unit tests
• Did you add logging beneficial for troubleshooting of customer issues?
• Did you add new logging? We would like the logging between platforms to be similar. Refer to Logging from iOS SDKs → Things to consider for newly added logs in Confluence for more information.

[EgorovEI]

!squash