Blender Git Loki

Fix T79737: ERROR ACCESS VIOLATION when switching to eevee rendered view

This prevents Blender from crashing when switching
to rendered view and the grid_data is NULL in the
lightcache (due to possible corruption), by switching
to the fallback lightcache. The fix extends the solution
for possible corruption in the cube_data as well.

Fix T79737

Reviewed By: fclem
Differential Revision: https://developer.blender.org/D8835