The copy_node_graph() method checks for a "window" key in the context
override, but get_shader_editor_context() wasn't providing it. This
caused the function to return early, preventing external styles from
loading.
Updated get_shader_editor_context() to include the window when the
screen differs from the current context, following the same pattern
used in get_viewport_context().
Ryan Schultz
d69b4927a2