[B1.2] Crash after weird lightmap calculation

[TMarc]

To respond to a different topic, I created a very small map with lights in it.
I let calculate lightmap in high quality, and after saving, it came out like this.

TMC_B1.2_Weird_lightmap.png

TMC_B1.2_Weird_lightmap2.png

Lights.gbx

Then I exited the editor, loaded the map, and it was displayed fine.

Lichter.gbx

Then I saved with a different file, and when I exited the editor, it crashed.