Fixed Tiberian Sun construction yard flickering

as described in #5765.
All the brackets here are unnecessary, and it might pay to add a comment to reduce future confusion:
```csharp
// Note: the mixed Integer / fp division is intentional, and required for calculating the correct offset.
Offset = new float2(x + width / 2 - 0.5f * frameSize.Width, y + height / 2 - 0.5f * frameSize.Height);
```