Fix EZP-23603: ignore node visibility when checking subtree count

JIRA: https://jira.ez.no/browse/EZP-22310

When `eZSolr::updateNodeVisibility()` is called, a pending action is created if the node has any child nodes.
However, this only works when `IgnoreVisibility` is `true` (admin siteaccess).

This fix specifically sets the `IgnoreVisibility` param. to count child nodes, so that the function works properly f.e. in a frontend siteaccess.