Incomplete safeguard against empty objects in level component (master)

[Emprah]

I was able to trigger an error by left clicking into a solitary level component without any items in it.

itemNearCursor will be null, but only undefined is catched in line 186:
if (itemNearCursor.current !== undefined && itemNearCursor.nearest !== undefined) {

This later leads to an error in line 472, when items[0] contains null:
start: items[0].samplePoint,

[Emprah]

The same check is missing under the same premises for right clicks, in line 227.