Fix wesnoth.set_village_owner ignoring the fire_event parameter

Looks like this was lost in the refactor that introduced the luaW_checklocation helper function.
If the location is specified as two separate parameters for x and y, this helper function
actually pops the y parameter from the stack so that further parameter tests can act
as if the location was a single parameter. Thus, the fire_event parameter, which used to
be 4th on the stack, is now moved down to 3rd.

src/scripting/game_lua_kernel.cpp

@@ -1178,7 +1178,7 @@ int game_lua_kernel::intf_set_village_owner(lua_State *L)
 
 	// If the new side was valid, re-assign the village.
 	if(new_side) {
-		new_side->get_village(loc, old_side_num, (luaW_toboolean(L, 4) ? &gamedata() : nullptr));
+		new_side->get_village(loc, old_side_num, (luaW_toboolean(L, 3) ? &gamedata() : nullptr));
 	}
 
 	return 0;