Areastore: fix "attempt to index a number value"

Before, calling get_areas_in_area for an areastore with both
include_borders and include_data would result in a lua error,
if there was at least one area as result:
attempt to index a number value in function 'get_areas_in_area'

src/script/lua_api/l_areastore.cpp

@@ -45,6 +45,7 @@ static void push_area(lua_State *L, const Area *a,
 {
 	if (!include_borders && !include_data) {
 		lua_pushboolean(L, true);
+		return;
 	}
 	lua_newtable(L);
 	if (include_borders) {