Now it is possible to save Draft with fields filled with only space symbols

Preconditions
User is logged in and has permissions to send private messages

Steps to reproduce
1. User opens private messages page and click "Compose" button
2. User fill all fields with one space
3. User click "Save" button

Actual result
Message is saved in Drafts with "not specified" to and subject fields
When user opens this draft - all fields are empty (e.g. without spaces)

Expected result
User receives message like "Can't save blank message"