Update scene.py for display_type "none" bug

[jadenecke]

using display_type='none' would not render because the offscreen renderer flag would not be set.

code to reproduce error:

import yabplot
yabplot.plot_tracts(atlas='xtract_tiny', display_type='none', export_path="testTract.png")

results in

RuntimeError: Nothing to screenshot - call .show first or use the off_screen argument

I think it was just missing the off_screen flag if 'none' was specified in the plotter call, at least that seemed to fix it for me.

[jadenecke]

I think this is not perfect yet, as the fix only allows for the exporting if the display_type is 'none'. However, otherwise the finalize_plot functionality needs to be reworked as the screenshot can not be taken before either a .show or a .render command is called, but the show opens the window, and the render requires the background flag to be set to true.
So far, the only solution I can think of is to create two plotters, one for the screenshot and the other for the viewer, but that doubles the compute time and that is not ideal. I don't know if there is a way to call the screenshot on the plotter somehow reactively, the moment the plotter calls show, or something like that.

[teanijarv]

I couldn't reproduce the error. It seems to be working for me currently too even though the changes you made make sense I think. Are you with the latest version bc I made some changes in there I think with the latest release