wrtd_attr_set_rule_enable() does not check if SOURCE and DESTINATION are defined
wrtd_attr_set_rule_enable() will enable a rule even if the SOURCE/DESTINATION are invalid. This can cause segfaults when at the end of the function we call wrtd_reconfigure().
The function should check that both SOURCE and DESTINATION are valid, otherwise return an error like WRTD_ERROR_UNKNOWN_CHANNEL_NAME
.