Copy lastmessage to the newly created context.
Copy lastmessage to the newly created context.

This fixes a case where the first user message
gets lost when OTRL_POLICY_REQUIRE_ENCRYPTION
policy is set because after establishing the
encryption lastmessage remains with the master
context and will not be resent.

[Slightly modified by Ian Goldberg]

DrWhax/libotr-ci-test,DrWhax/libotr-ci-test,DrWhax/libotr-ci-test,DrWhax/libotr-ci-test