Sculpt: Fix #104618 (again).

SculptAttributeParams.stroke_only wasn't being
applied to existing attributes properly.

source/blender/blenkernel/intern/paint.cc

@@ -2719,6 +2719,11 @@ static SculptAttribute *sculpt_attribute_ensure_ex(Object *ob,
   if (attr) {
     sculpt_attr_update(ob, attr);
 
+    /* Since "stroke_only" is not a CustomData flag we have
+     * to sync its parameter setting manually. Fixes #104618.
+     */
+    attr->params.stroke_only = params->stroke_only;
+
     return attr;
   }