[TESTING]Factory exploit part 2

[Giacomo]

I'm still finding I can exploit production at a factory. The situation is certainly better than it was, but the problem still persists....

This is what I do...

Two models being produced at a factory
Drop one model's production to zero. Press assign.
Go to the other model and add the spare capacity there. Press assign.
On this same model, drop the production to zero. Assign.
Now return to the original model and you find you have more assembly lines than the factory allows.

[Eric.B]

I haven't been able to duplicate this, however I assume it's similar issues to the last one.

I have included a number of conditional checks to make sure factories can not get negative lines in use. This should prevent this bug.

IF it reappears in 1.11 please let me know (and include the save with the extra lines assigned to production!)