pcre: fix var capture for non relative matches

Var capture setup depended on the match being relative due to a logic
error.

https://redmine.openinfosecfoundation.org/issues/1327

Prscript:
- PR build: https://buildbot.openinfosecfoundation.org/builders/inliniac/builds/65
- PR pcaps: https://buildbot.openinfosecfoundation.org/builders/inliniac-pcap/builds/65