Fix url parsing for returned Windows paths

[bnavigator]

The file: URL schema for windows paths retains a leading / when parsed with urllib.parse, this does not work with subsequent loads.

Before:

(.win-venv) C:\Users\Greiner\Documents\testfiles\g12>ds9samp_get --debug "fits header"
# Connected: Connection to DS9 8.7 (client c1)
# Command: fits header
DEBUG: ds9.get fits header timeout=10
DEBUG: {'samp.result': {'url': 'file://localhost/C:/Users/Greiner/AppData/Local/Temp/ds982491346065.fits.txt'}, 'samp.status': 'samp.ok'}
DEBUG: DS9 returned data in URL=file://localhost/C:/Users/Greiner/AppData/Local/Temp/ds982491346065.fits.txt
# ds9samp_get (0.1.1): ERROR [Errno 22] Invalid argument: '/C:/Users/Greiner/AppData/Local/Temp/ds982491346065.fits.txt'

After:

(.win-venv) C:\Users\Greiner\Documents\testfiles\g12>ds9samp_get --debug "fits header"
# Connected: Connection to DS9 8.7 (client c1)
# Command: fits header
DEBUG: ds9.get fits header timeout=10
DEBUG: {'samp.result': {'url': 'file://localhost/C:/Users/Greiner/AppData/Local/Temp/ds992336956101.fits.txt'}, 'samp.status': 'samp.ok'}
DEBUG: DS9 returned data in URL=file://localhost/C:/Users/Greiner/AppData/Local/Temp/ds992336956101.fits.txt
XTENSION= 'IMAGE   '           /extension type
BITPIX  =                  -64 /bits per data value
NAXIS   =                    3 /number of axes
(...)

I tested on Linux as well, the parsed paths still work.

[bnavigator]

Any progress here?