Fix EZP-22792: consecutive calls to trashNode::originalParent() return null

JIRA: https://jira.ez.no/browse/EZP-22792

The `originalParent()` function was saved `pathArray` property after the first call, but used `array_pop()` on every consecutive call.
This caused all the function to always return `null` on consecutive calls, as `$thisParentPath` would keep getting smaller.