archive: fix listing for 7z multi-volumes archives

git-svn-id: svn://svn.code.sf.net/p/mcomix/code@1079 ef8490bc-f317-4725-81ed-e95a9aca1bcf
archive: yet another fix for archives within archives

An archive contents must be *fully* listed before attempting any
extraction.

git-svn-id: svn://svn.code.sf.net/p/mcomix/code@1080 ef8490bc-f317-4725-81ed-e95a9aca1bcf
archive
core
thumbbar