fix bug on end of sstream crash due to "has not method end()"

[matteocrippa]

I was experiencing an error using stream on missing method end, in this way we avoid that.

hope this helps.

[peterbraden]

Is this right? Should we be reading into a buffer on .write and only creating the matrix on .end?

[danschultzer]

@peterbraden I guess this is safe to close since it's more than 3 years old?

[peterbraden]

I think so. I don't think node streams require an end method, but if I'm wrong we can reopen for sure.

See https://nodejs.org/api/stream.html#stream_class_stream_writable