First frame of ZergBirth order has a Zerg Egg with no BuildType

[Cmccrave]

Just on the first frame the order occurs, the type of the unit stays as Zerg Egg, but the BuildType is now UnitTypes::None.

Possibly related to #613

[NiteKat]

This was documented on 4.4. Appears to be related to this switch: https://github.com/bwapi/bwapi/blob/v4.4.0/bwapi/BWAPI/Source/BWAPI/UnitUpdate.cpp#L567

There is no case for the ZergBirth order, and since the type is still ZergEgg, there is no buildUnit, and the supply for the egg is 0.

[NiteKat]

Adding ZergBirth into the switch case appears to resolve the issue, and verified I don't see any weird effects with Lurkers, Guardians, or Devourers. I cannot think of any other cases to test for side effects from this change.