GPv3: Avoid unnecessarily creating cyclic attribute in hard erasor

If the attribute didn't already exist (none of the initial curves
were cyclic), none of the result curves will be cylic either.

source/blender/editors/sculpt_paint/grease_pencil_erase.cc

@@ -538,8 +538,10 @@ struct EraseOperationExecutor {
                            {"cyclic"},
                            dst_to_src_curve,
                            dst_attributes);
-    array_utils::gather(
-        src_now_cyclic.as_span(), dst_to_src_curve.as_span(), dst.cyclic_for_write());
+    if (src_cyclic.get_if_single().value_or(true)) {
+      array_utils::gather(
+          src_now_cyclic.as_span(), dst_to_src_curve.as_span(), dst.cyclic_for_write());
+    }
 
     /* Display intersections with flat caps. */
     if (!keep_caps) {