Fix T85252: Gpencil interpolate sequence crash in new scenes

The value of the step was not initializated for new scenes.

source/blender/blenkernel/intern/scene.c

@@ -167,6 +167,8 @@ static void scene_init_data(ID *id)
                      &gp_primitive_curve->clipr,
                      CURVE_PRESET_BELL,
                      CURVEMAP_SLOPE_POSITIVE);
+  /* Grease pencil interpolate. */
+  scene->toolsettings->gp_interpolate.step = 1;
 
   scene->unit.system = USER_UNIT_METRIC;
   scene->unit.scale_length = 1.0f;