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### Description

I am working on extending $hfl and $hflc to support some more headers.

During some experimentation, I stumbled into some weird behavior regarding $(hfl(Route)[-1]) and negative indexing of $hfl pseudo-variable (also for Via, Contact).

Per the [docs ](https://www.kamailio.org/wikidocs/cookbooks/devel/pseudovariables/#hflname-h... ): -1 index should print the last header found and so on (as stated by $hdr $hfl).

Right now, -1 produces null, and from -2 and onwards it prints correctly from the last one to the first one.

### Troubleshooting

#### Reproduction ``` #kamailio.cfg ... request_route { xlog("L_INFO", "Route headers hdr: $hdr(Route)\n"); xlog("L_INFO", "Route headers hfl: $hfl(Route)\n"); xlog("L_INFO", "Route headers count: $hflc(Route)\n"); xlog("L_INFO", "Route headers 0: $(hfl(Route)[0])\n"); xlog("L_INFO", "Route headers 1: $(hfl(Route)[1])\n"); xlog("L_INFO", "Route headers 4: $(hfl(Route)[4])\n"); xlog("L_INFO", "Route headers -1: $(hfl(Route)[-1])\n"); xlog("L_INFO", "Route headers -2: $(hfl(Route)[-2])\n"); xlog("L_INFO", "Route headers -3: $(hfl(Route)[-3])\n"); ... } ```

Seng a SIP message containing Route (but also applicable for VIA, Contact headers): ``` OPTIONS_MSG_2CONTACTS="OPTIONS sip:example.com SIP/2.0 Via: SIP/2.0/UDP 192.168.1.100:5060;branch=z9hG4bK123456789 Max-Forwards: 70 From: sip:bob@example.com;tag=123456789 To: sip:alice@example.com Call-ID: 987654321@192.168.1.100 CSeq: 1 OPTIONS Contact: sip:bob@example.com;expires=3600,sip:bob2@example.com;expires=3600,sip:bob3@example.com;expires=3600 Route: sip:server1.example.com;lr;ftag=1234, sip:server2.example.com;lr;ftag=5678, sip:server3.example.com;lr;ftag=9012 Route: sip:server4.example.com;lr;ftag=1234, sip:server5.example.com;lr;ftag=5678 Content-Length: 0 "

echo -e "$OPTIONS_MSG_2CONTACTS" | nc -u localhost 5060 ```

See logs for logging details.

#### Log Messages

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``` INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers hdr: sip:server1.example.com;lr;ftag=1234, sip:server2.example.com;lr;ftag=5678, sip:server3.example.com;lr;ftag=9012 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers hfl: sip:server1.example.com;lr;ftag=1234 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers count: 5 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers 0: sip:server1.example.com;lr;ftag=1234 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers 1: sip:server2.example.com;lr;ftag=5678 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers 4: sip:server5.example.com;lr;ftag=5678 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers -1: <null> INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers -2: sip:server5.example.com;lr;ftag=5678 INFO: {1 1 OPTIONS 987654321@192.168.1.100} <script>: Route headers -3: sip:server4.example.com;lr;ftag=1234 ```

### Possible Solutions

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In https://github.com/kamailio/kamailio/blob/e59c4415707f0995a0d5315b5601ae518b..., the count should start at 0 ie. ``` n=0; // not n=1; ```

### Additional Information

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

``` (paste your output here) ```

* **Operating System**:

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``` (paste your output here) ```