Describe the bug
The app crashes when the user taps on the image size options in the gallery block.

To Reproduce
Steps to reproduce the behavior:

• Create a gallery block with some images
• Tap the gallery
• Tap the gallery settings icon (the gear)
• Tap "Images size" option
• 💥

Expected behavior
The app should not crash

Smartphone (please complete the following information):

• Device: iPhone11
• OS: iOS 13.3
• Version 14.0 (beta)

Additional context
The size option was added for web, but has not yet been implemented / tested on mobile.