Critical error when "Gap Between Cards" is set to 0

[emarufh]

Description:
Setting the "Gap Between Cards" option to 0 in the Showcase settings tab triggers a critical error on the frontend/backend.

Steps to Reproduce:

1. Go to WC Category Showcase settings → Add/Edit a Showcase → Showcase tab
2. Set "Gap Between Cards" to 0
3. Save settings and view the showcase on the frontend

Expected Behavior:
Cards should display with no gap between them.

Actual Behavior:
A critical error is thrown.