Bug in effectutilities.lua

Bug 3778. Need to add a check for nil or on unit death..
```
warning: Error running lua script: ...a\faforever\gamedata\lua.nx2\lua\effectutilities.lua(345): attempt to loop over field `BuildEffectBones' (a nil value)
stack traceback:
...a\faforever\gamedata\lua.nx2\lua\effectutilities.lua(345): in function <...a\faforever\gamedata\lua.nx2\lua\effectutilities.lua:341>
...ata\lua.nx2\lua\sim\units\cybran\cairfactoryunit.lua(62): in function <...ata\lua.nx2\lua\sim\units\cybran\cairfactoryunit.lua:56>
```