Fix collection indexing starting from -1 for new databases.

Normally, indexing starts with 1. But as the Recent collection
was inserted with id -2, the backend got confused and started adding
collections with -1, 0, and so forth.

git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@863 ef8490bc-f317-4725-81ed-e95a9aca1bcf