Sufficiently long event in mixed-length slot bleeds over to next slot

[iansltx]

Found this in https://joind.in/event/bulgaria-php-conference-2019/schedule/grid at Lunch. There's a 40 minute event there, up against lunch, which is 90 minutes, followed by 40 minute talk sessions. If I bump the length of lunch to >= 80 minutes, the grid displays it as if lunch is still happening with the next round of talks.

Guessing this will require another rather significant rework of the grid display code. Or pull schedule grid resolution up into a helper that isn't necessarily looking at things one row at a time. Either way, this is definitely another tricky edge case where solving the problem is a good bit harder than reproducing it.