Block restaurant dish edit if there are open enrollments that use that restaurant

[Kurocon]

Recently, the dishes for Oh My Grill were edited, where all old dishes were removed, and new ones were added.
There were also still a few activities with open enrollments, that used Oh My Grill as a restaurant.
This created a situation where those old enrollments could not select any dish for the food option.
Also, any enrollments that already had participants with selected food options, would generate a 500 error because the dish prices could not be retrieved.

When we create a food enrollment option, we create a copy of the current prices of the dishes (DishPrice), so that existing enrollments keep the old price. So, on the activity enrollment, only the dishes and prices that existed when the enrollment was created are shown. However, if the enrollment is still open, and all of the dishes that existed when it was created were made unavailable, then no dishes are now shown due to the model filter and enrollment becomes impossible!

The easiest way to prevent this is to prevent editing a restaurant's dishes if there are any open enrollments that use that restaurant.

This may be a bit overkill though (because now to edit the restaurant you need to wait for those enrollments to close, or remove the option), maybe an alternative option exists? Open for suggestions.