.close is called for the second time without any error

[xSAVIKx]

Describe the bug
If you use the streamer with the following example:

    with importer.ImportStreamer() as streamer:
        streamer.set_sketch(sketch)
        streamer.set_timeline_name(timeline_name)
        streamer.add_file(path)

        streamer.close()  # <-- this uploads the data

the data is going to be uploaded twice. Cause in the close there's no check if the streamer was previously closed or not.

To Reproduce
Steps to reproduce the behavior:

1. Run the provided example
2. See that events are duplicated

Expected behavior
An error is raised if the importer was already closed.

Additional context
I get that this may be the desired behavior but I saw a line somewhere about calling .close and added it and then only noticed duplicated data. IMO failing (or doing nothing) in such a situation is a better practice. That's how other closable classes usually behave