i_system: "fix" recursive i_quit

well this still aint working all to great, but atleast this allows me to quit the game if it gets stuck without having to always send a kill signal to it

src/sdl/i_system.cpp

@@ -1952,17 +1952,19 @@ INT32 I_StartupSystem(void)
 	return 0;
 }
 
+boolean is_quitting = false;
+
 //
 // I_Quit
 //
 void I_Quit(void)
 {
-	static SDL_bool quiting = SDL_FALSE;
-
 	/* prevent recursive I_Quit() */
-	if (quiting) goto death;
+	if (is_quitting)
+		abort();
+
+	is_quitting = true;
 	SDLforceUngrabMouse();
-	quiting = SDL_FALSE;
 	M_SaveConfig(NULL); //save game config, cvars..
 	D_SaveBan(); // save the ban list
 
@@ -1997,7 +1999,7 @@ void I_Quit(void)
 	}
 	if (myargmalloc)
 		free(myargv); // Deallocate allocated memory
-death:
+
 	W_Shutdown();
 	exit(0);
 }