fix #1961 use bpy.context.window.scene instead of bpy.context.scene

[kaosat-dev]

Hi !
This is a tiny PR to fix #1961
Ensures that the exporter uses bpy.context.window.scene instead of bpy.context.scene
It also fixes additional issues when you create scenes to export dynamically , and bpy.context.scene does not sync with
bpy.context.window.scene (which , unlike the first, is user settable).

Thanks for this fantastic tool btw :)

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