Error when deleting a panelized entity

(Continued from #1623536: Multiple errors when attempting to save content when "Allow panel choice" is checked.)

When deleting an entity, Panelizer deletes corresponding records from {panelizer_entity}. However, it does not verify that the query to obtain a list of display IDs ("did" values) returns all relevant data, it can return a bunch of "0" values which will cause the following error:

Warning message
The reverted panels display(s) were exported, please run a string refresh to update the translatable strings.

(allegedly)