satin: skip contour underlay if there are no pairs (inkstitch#3912)

kaalleen · web-flow · commit 2417b351d29f · 2025-08-19T13:59:02.000+02:00
diff --git a/lib/elements/satin_column.py b/lib/elements/satin_column.py
@@ -1353,6 +1353,9 @@ def do_contour_underlay(self, end_point):
             self.contour_underlay_stitch_tolerance,
             -self.contour_underlay_inset_px, -self.contour_underlay_inset_percent/100)
 
+        if not pairs:
+            return []
+
         first_side = running_stitch.even_running_stitch(
             [points[0] for points in pairs],
             self.contour_underlay_stitch_length,
