Emitting of an error from Messenger in Child process is never handled

[lucasnetau]

In a Child Process the Messenger class can emit errors in crashed() and iterateMessages() however there is no listener for these error events. The RPC message is never responded to and the parent waits forever.

A quick fix is adding the following in the Process::create() factory

$messenger->on('error', function($throwable) use(&$reject, $messenger) {
    $reject($throwable);
});

This will terminate the child process and the parent process will reject the RPC call with CommunicationWithProcessUnexpectedEndException

There may be a better way however I don't know the code well enough and if the error occurs in MessagesFactory::fromLine due to an invalid rpc method then we can't cleanly handle the error.