Minimal change to stop blender window opening across all monitors.
Workaround the problem by starting maximized, and using sane defaults for non maximized window.
I checked on a few different solutions to this, Using Xinerama works OK, but with different size monitors
and not knowing which one the window-manager will pick in advance - this can be wrong too.
Now instead of opening with the screen size, just start maximized and use a default size for the non-maximized window (clamped by the screen size).
This isn't perfect since you could have 2x monitors at 1024x768, open blender, un-maximize - and blender window would cross over into the second monitor.
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