Reset game.activeactivity and game.act_fade in scriptclass::hardreset()

Resetting game.activeactivity fixes triggering Undefined Behavior if you
quit to the menu while standing inside an activity zone, and then
re-entered the game. Resetting game.act_fade also fixes the activity
zone prompt fadeout that happens once the above segfault is fixed.

Don't worry, other activity-zone like variables such as teleporter
prompts and trophy text are already covered. obj.trophytext is reset in
scriptclass::hardreset(), too, and game.readytotele is reset every time
mapclass::gotoroom() is called, and mapclass::gotoroom() is called every
time a gamemode is started.

desktop_version/src/Script.cpp

@@ -3503,6 +3503,9 @@ void scriptclass::hardreset()
 	game.flashlight = 0;
 	game.screenshake = 0;
 
+	game.activeactivity = -1;
+	game.act_fade = 5;
+
 	//dwgraphicsclass
 	graphics.backgrounddrawn = false;
 	graphics.textboxremovefast();