fixed return value from Space::add_child_space()

src/space/space.cpp

@@ -2028,7 +2028,7 @@ Space & Space::add_child_space()
 	TableType * child_table = find_child_space_table();
 	child_table->push_back(new Space());
 
-	return child_table->back();
+	return *child_table->back();
 }