gedia created an issue (kamailio/kamailio#4242)

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### Description This is definitely not high priority, just a nuisance when auditing logs for actionable events.

The following is logged (see Log Messages section below) on edge proxies when the outbound module is loaded and the REGISTER contains: ``` Contact: * Expires: 0 ```

AFAIK this is legit when a UAC asks that all their contacts be removed from the location database.

### Troubleshooting

#### Reproduction Force a UAC to send an unREGISTER towards an outbound-capable kamailio edge proxy.

#### Log Messages

``` outbound [outbound_mod.c:325]: use_outbound_register(): empty Contact: ```

#### SIP Traffic

<!-- If the issue is exposed by processing specific SIP messages, grab them with ngrep or save in a pcap file, then add them next, or attach to issue, or provide a link to download them (e.g., to a pastebin site). -->

See description

### Possible Solutions

<!-- If you found a solution or workaround for the issue, describe it. Ideally, provide a pull request with a fix. --> I'm not sure what the best approach would be here, but I'm thinking one of the following: * Either handle this case gracefully (contact is * in REGISTER with Expires=0), without logging anything, unless there's some misbehaviour here by the UAC I'm not aware of regarding outbound and unREGISTER behaviour * Or, log this in a more verbose level (e.g. debug), when contact parsing fails due to it being set to '*' ### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` version: kamailio 5.8.6 (x86_64/linux) flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, MEM_JOIN_FREE, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLOCKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_SEND_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: unknown compiled with gcc 10.2.1 ```

* **Operating System**:

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``` No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux 11 (bullseye) Release: 11 Codename: bullseye Linux lbpub0-tis0-cn1 5.10.0-21-amd64 #1 SMP Debian 5.10.162-1 (2023-01-21) x86_64 GNU/Linux ```