Xpra: Ticket #2143: non-xshm capture error

$ XPRA_XSHM=0 ./xpra/x11/shadow_x11_server.py test.png
2019-02-12 21:06:49,509 CUDA initialization (this may take a few seconds)
2019-02-12 21:06:49,616 CUDA 10.0.0 / PyCUDA 2018.1.1, found 1 device:
2019-02-12 21:06:49,617   + GeForce GTX 1070 @ 0000:01:00.0 (memory: 83% free, compute: 6.1)
Traceback (most recent call last):
  File "./xpra/x11/shadow_x11_server.py", line 201, in <module>
    v = main(sys.argv[1])
  File "./xpra/x11/shadow_x11_server.py", line 185, in main
    pil_image = Image.frombuffer("RGBA", (w, h), pixels, "raw", fmt, image.get_rowstride())
  File "/usr/lib64/python2.7/site-packages/PIL/Image.py", line 2479, in frombuffer
    return frombytes(mode, size, data, decoder_name, args)
  File "/usr/lib64/python2.7/site-packages/PIL/Image.py", line 2412, in frombytes
    im.frombytes(data, decoder_name, args)
  File "/usr/lib64/python2.7/site-packages/PIL/Image.py", line 810, in frombytes
    d = _getdecoder(self.mode, decoder_name, args)
  File "/usr/lib64/python2.7/site-packages/PIL/Image.py", line 456, in _getdecoder
    return decoder(mode, *args + extra)
ValueError: unknown raw mode