[reSIProcate] expires Contact parameter can be parsed as negative if too large

[Byron Campen <bcampen@xxxxxxxxxxxx>]

In the scalar02 torture-tests case, an over-large Contact expires param will be parsed as negative, and can be re-emitted. 

*snip*

In case scalar02:

Original text:

REGISTER sip:example.com SIP/2.0

Via: SIP/2.0/TCP host129.example.com;branch=z9hG4bK342sdfoi3

To: <sip:user@xxxxxxxxxxx>

From: <sip:user@xxxxxxxxxxx>;tag=239232jh3

CSeq: 36893488147419103232 REGISTER

Call-ID: scalar02.23o0pd9vanlq3wnrlnewofjas9ui32

Max-Forwards: 300

Expires: 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Contact: <sip:user@xxxxxxxxxxxxxxxxxxx>

  ;expires=280297596632815

Content-Length: 0

Encoded form:

REGISTER sip:example.com SIP/2.0

Via: SIP/2.0/TCP host129.example.com;branch=z9hG4bK342sdfoi3

Max-Forwards: 300

Contact: <sip:user@xxxxxxxxxxxxxxxxxxx>;expires=-559038737

To: <sip:user@xxxxxxxxxxx>

From: <sip:user@xxxxxxxxxxx>;tag=239232jh3

Call-ID: scalar02.23o0pd9vanlq3wnrlnewofjas9ui32

CSeq: 0 REGISTER

Expires: 0

Content-Length: 0

*snip*

Best regards,

Byron Campen

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