progress not updated when building supply depots

The SCV with orders to build a supply depot will go about building the depot through completion, but the orders list will show the progress as zero the whole time.
The code below is a snippet of the code illustrating the problem: with const *iUnit pointing to the SCV that is doing the building

```
if (iUnit != NULL)
{
if (!iUnit->orders.empty())
{
auto &o = *iUnit->orders.begin();
std::cout << "\nprogress on " << AbilityTypeToName(o.ability_id) << " " << o.progress;
}
}
```