fix: Port merged TheSuperHackers file and handle leak fixes

[tintinhamans]

Ports three merged upstream fixes for leaked file and system handles. Each is a cherry-pick -x of the upstream commit.

• fix(addoncompat): Close fullviewport.dat file handle after reading it TheSuperHackers/GeneralsGameCode#3476 fix(addoncompat): Close fullviewport.dat file handle after reading it
• fix: Close leaked system handles in GameWindowManager, ImageCollection, MainMenuUtils TheSuperHackers/GeneralsGameCode#3497 fix: Close leaked system handles in GameWindowManager, ImageCollection, MainMenuUtils
• fix(maputil): Close the file and free the buffer when a map preview copy fails TheSuperHackers/GeneralsGameCode#3485 fix(maputil): Close the file and free the buffer when a map preview copy fails

The ImageCollection part of TheSuperHackers#3497 is already on this branch (same FindClose fix), so only the GameWindowManagerScript.cpp and MainMenuUtils.cpp parts are new. GameWindowManagerScript.cpp exists once per game here, so it is changed in both the Generals and GeneralsMD copies.

Zero Hour (z_generals) builds here. The Generals copy of GameWindowManagerScript.cpp was not compiled, g_generals does not build on this branch.