[native] Create a thread before sending a message to a pending thread

Test Plan: I tested sending messages in already created threads. In a pending thread, sending a message resulted in an alert - which was expected without the next diff which allows creating a pending thread. With the next diff, sending a message resulted in creation of a new personal thread.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian

Differential Revision: https://phabricator.ashoat.com/D327