SigMF archive error reading data file

[Deschain]

I think that there is an error opening sigmf archive files. The compliant dataset file is no recognized as a valid file because the relative path of the tar member is used https://github.com/gnuradio/SigMF/blob/1eef44a67636ab15078e7eecc00144b9e18cdaa3/sigmf/sigmffile.py#L779