Fix frametime dependence on FPS (bxt_fix_fpsbug)

[ScriptedSnark]

See ValveSoftware/halflife#1940

This bug affects only Pre-Steampipe engine builds (Windows). High FPS often leads to game speed change (not exactly game, but movecmd speed) which could be an issue for segmenting/TASing and so on.

To reproduce, just type developer 1;fps_max 501 in console.

Fix proposed links:
ValveSoftware/halflife#1940 (comment)
https://github.com/tmp64/BugfixedHL-Rebased/blob/master/src/game/client/engine_patches_windows.cpp#L463-L520