Relax dialog checking in get_sip_pvt_byid_locked so it works when the dialog is forked.

(closes issue ASTERISK-20638)
Reported by: eelcob
Patches:
      pedantic-call-pickup-from-tag.patch uploaded by eelcob (license 6442)
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Merged revisions 382171 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 382174 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@382182 65c4cc65-6c06-0410-ace0-fbb531ad65f3