Fix: Grease Pencil: Uninitialized attribute values when drawing strokes

When drawing strokes in Grease Pencil, some (custom) attribute values
stayed uninitialized. This was due to a tiny bug in the Draw operator
initializing only some attribute values of newly drawn stroke points
to their default value and not all of them.
This PR fixes that.

Pull Request: https://projects.blender.org/blender/blender/pulls/133216

source/blender/editors/sculpt_paint/grease_pencil_paint.cc

@@ -980,7 +980,7 @@ struct PaintOperationExecutor {
         attributes,
         bke::AttrDomain::Point,
         bke::attribute_filter_from_skip_ref(point_attributes_to_skip),
-        curves.points_range().take_back(1));
+        curves.points_range().take_back(new_points_num));
 
     drawing_->set_texture_matrices({self.texture_space_}, IndexRange::from_single(active_curve));
   }