You can drag-to-create events beyond the calendar

[ziggabyte]

I can drag to create an event beyond the confines of the calendar. I discovered this when looking at the great and quick work of @troldmand when reviewing #1613

Steps to reproduce:

• go to the weekly calendar
• drag to create an event
• keep dragging downwards

expected

• the event stops when the calendar stops

actual

• the event keeps going beyond the calendar, and when releasing the click the created event is 0 minutes long, or the whole calendar disappers