In CLI mode, PartPlateList is constructed with a NULL plater pointer
(OrcaSlicer.cpp:3612). When set_shapes() calls PartPlate::set_shape(),
it unconditionally executes render data preparation code that
dereferences the null plater through calls like generate_print_polygon()
→ wxGetApp().plater(), causing a segmentation fault (exit code 139).
This adds a null check on m_plater in PartPlate::set_shape() to skip
the render-only code block that generates logo triangles, print/exclude
polygons, gridlines, icon vertices, and plate name textures.
These rendering operations are not needed in CLI mode and this change
has no impact on GUI mode where m_plater is always valid.
