Crash at because rendering null assimilator sprite

[DRed96]

Class: Critical
Type: Crash/Hang
Frequency: Unknown

STEPS TO REPRODUCE:

1. Play the rest of the game normally. Create and assimilator and a nexus in the expansion.
2. Destroy the down-right base.
3. Wait for the Zergs to attack you.
4. They Destroy the main assimilator.

RESULTS:
The game crashes at render because the passing a NULL texture. Can't remember the exact line
ADDITIONAL INFO:
Hard to reproduce.