Win32 path separator on AsyncFileStreamer::streamFile

[mbsteixeira]

In the method "AsyncFileStreamer::streamFile", the "auto it = asyncFileReaders.find(url);" fails because of the windows plataform path separator.
It's necessary a change from '/' to '\' , so the search succeeds.

[ghost]

Yes one could work on that however it is just a simple example and could be solved in a cross platform way if wanted

[mbsteixeira]

Ok.

[ghost]

Feel free to PR though