Url events don't work when an "action" option is configured
```
<event-bindings>
<event type="url" trigger="source-connect">
...
...
<option name="action" value="mount_add" />
```
Bug is in event_url.c:event_get_url()
https://gitlab.xiph.org/xiph/icecast-server/blob/master/src/event_url.c#L134
Should be `free(self->action)` not `free(self->url)`
issue