Fix button placement in minimized in-game windows

[falbrechtskirchinger]

As mentioned, I've discovered a bug introduced in 938f355891d #1609. This is a very quick fix. Let me know if you'd prefer to store the full size in IngameWindow and add a GetFullSize() member function, or maybe a different solution entirely.

Commit message follows:

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Some windows position their buttons based on GetSize().y, which results in incorrect placement if the window is persisted and minimized. Replace uses of GetSize().y with the full window height.

Affected windows:

• iwBuildings
• iwDistribution
• iwWares

[Flamefire]

Let me know if you'd prefer to store the full size in IngameWindow and add a GetFullSize() member function, or maybe a different solution entirely.

Sounds more reasonable to me as it has less constants floating around. That member function looks easy to implement too: combine iwHeight and contentOffset + contentOffsetEnd similar to what is done (in reverse) in https://github.com/Return-To-The-Roots/s25client/blob/master/libs/s25main/ingameWindows/IngameWindow.cpp#L89C20-L89C29