Make conversation::send_message work without an error.
This MR makes SendMsgAndInstallHandler tolerate the case where handler
is None but msg
is set.
Previously it was possible for handler
to be None only when
msg
was also None, which would make SendMsgAndInstallHandler into
a no-op. Now, if msg
is present but handler
is absent, we
use the previously installed handler, which I think was our
intention.
Without this MR, Conversation::send_message
simply won't work.
Fixes #1085 (closed).
cc @gabi-250 who has worked on these APIs, and @Diziet who wrote 77903a29 and may have intended a different solution here.