Rebuilt Grilles on Dropships are Invisible

[Nickvr628]

Bug Description:
Grilles on the dropship windows get destroyed by xenos, when they are repaired the sprite is invisible, but they still exist and block movement, etc.

Steps to reproduce:
1. Trash Dropship
2. Try to rebuild grilles and windows
3. Become very confused as you cannot see your work
4. Realize it is bug

[phil235]

Confirmed. The grille is there, but sprite-less. This only happens sometimes, not sure why.