bgpd: Free memory for as-path filter if regexp is wrong

bgpd: Free memory for as-path filter if regexp is wrong

Before:

```
$ vtysh -c 'sh memory bgpd | include Temporary'; echo ; for x in $(seq 1 1000); do vtysh -c 'conf' -c 'bgp as-path access-list belekas permit wrong' >/dev/null; done; vtysh -c 'sh memory bgpd | include Temporary'
Temporary memory              :       19 variable       504       22       656
Temporary memory              :     1019 variable     24504     1023     24656
```

After:

```
$ vtysh -c 'sh memory bgpd | include Temporary'; echo ; for x in $(seq 1 1000); do vtysh -c 'conf' -c 'bgp as-path access-list belekas permit wrong' >/dev/null; done; vtysh -c 'sh memory bgpd | include Temporary'
Temporary memory              :       19 variable       504       22       656
Temporary memory              :       19 variable       504       24       680
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>