[ORC] Propagate errors to handlers when sendMessage fails.

[ORC] Propagate errors to handlers when sendMessage fails.

In SimpleRemoteEPC, calls to from callWrapperAsync to sendMessage may fail.
The handlers may or may not be sent failure messages by handleDisconnect,
depending on when that method is run. This patch adds a check for an un-failed
handler, and if it finds one sends it a failure message.