Crash when passing non-string header value to add_headers

[MayamaTakeshi]

If we try this:

    var oc = sip.call.create(gw1_t.id, {
        from_uri: `"${caller}"<sip:${caller}@test.com>`,
        to_uri: `sip:${prefix}${callee}@${c.server_ip1}`,
        headers: {
           'X-MyHeader1': 'abc',
           'X-MyHeader2': 'def',
           'Max-Forwards': 20,
        },
    })

sip-lab will segfault like this:

json_get_string_param from_uri
json_get_string_param to_uri
json_get_string_param request_uri
json_get_string_param proxy_uri
process_media call_id=0
i=0 media not found

create_media_endpoint call_id=0
create_media_transport
med_endtp->port=10000
create_media_endpoint call_id=0 type=1
i=0 media created 0x3aab9220

process_media call_id=0 call->local_sdp: v=0
o=- 3962149935 3962149935 IN IP4 0.0.0.0
s=pjmedia
t=0 0
m=audio 10000 RTP/AVP 0 8 3 120
c=IN IP4 127.0.0.1
b=TIAS:64000
a=rtcp:10001 IN IP4 127.0.0.1
a=sendrecv
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:3 GSM/8000
a=rtpmap:120 telephone-event/8000
a=fmtp:120 0-16


X-MyHeader1 => 'abc'
X-MyHeader2 => 'def'
close_media call_id=0
close_media_endpoint 0x3aab9220
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
audio_endpoint_remove_port
success
close_media_transport 0x3aab9e78
node: ../src/pjsip/sip_dialog.c:879: pjsip_dlg_terminate: Assertion `dlg->sess_count==0' failed.
Aborted (core dumped)
takeshi@takeshi-desktop:sip-lab$

Notice that it stopped before printing header Max-Forwards, so it is likely it properly detected Max-Forwards value is not a string and set_error and exited.
But then when performing the clean up of the media endpoint, it crashed and so we didn't see the error message as I think it would have been printed later.