Notice: Undefined index: pnid in _nodehierarchy_save_node() (Patch)

This patch fixes the below notice when generating content via the Devel module.

Notice: Undefined index: pnid in _nodehierarchy_save_node() (line 736 of /Volumes/Stuff/htdocs/php/undefeated.my/sites/all/modules/nodehierarchy/nodehierarchy.module)