If writing to buffer, winston 'logging' event will never be emitted

[JustinLivi]

On line 397 we attempt to write to the stream and invoke the winston-provided callback on response. However, if the stream is unavailable and we are writing to buffer on line 400 the callback is simply dropped and will never be invoked.

This results in the 'logging' event for the winston logger never firing for that transport and any buffered messages. To the end user it appears as though the messages themselves have been dropped, when in reality they have simply been buffered.

A potential relatively simple solution would be to simply retain references to the callbacks for buffered messages, and invoke these when the buffer has been successfully processed. If desired, I could make an attempt at implementing this change.