gameplay: make buffalo steak sandvich not reduce speed

the buffalo steak sandvich was made to not stack with other
movement speed bonuses. however, the way this was implemented
nullifies the greater of the two movement speed.

this fix makes it so if we are already above the berzerker speed cap,
we just don't apply berzerker speed at all and retain the faster speed.

if we are below the cap, then we boost by 35% speed like normal, up
to the berzerker cap of 135%

this only applies to MvM movement speed bonuses, since nothing
else can exceed the 135% cap in the base game.

ref: ValveSoftware/Source-1-Games#3476

Author: mastercoms

src/game/shared/tf/tf_player_shared.cpp

@@ -10561,12 +10561,17 @@ float CTFPlayer::TeamFortress_CalculateMaxSpeed( bool bIgnoreSpecialAbility /*=
 	if ( playerclass == TF_CLASS_HEAVYWEAPONS )
 	{
 		float heavy_max_speed = default_speed * 1.35f;
-		if ( m_Shared.InCond( TF_COND_ENERGY_BUFF ) )
-		{
+		// We don't stack with other speed boosts like the GRU, they make berzerker mode too fast
+		// but if we are already faster than the berzerker speed, then we won't shift the speed back down
+		// (like with MvM upgrades)
+		if ( m_Shared.InCond( TF_COND_ENERGY_BUFF ) && maxfbspeed <= heavy_max_speed )
+		{
+			// If we aren't already above the cap, then boost our speed by 35%, but only up to 135%.
+			// this means if we are slower than normal, we boost relative to that, but if we are faster
+			// than normal, we only boost up to the cap.
 			maxfbspeed *= 1.35f;
 			if ( maxfbspeed > heavy_max_speed )
 			{
-				// Prevent other speed modifiers like GRU from making berzerker mode too fast.
 				maxfbspeed = heavy_max_speed;
 			}
 		}