CLEANUP: cache: Fix leak of cconf->c.name during config check

CLEANUP: cache: Fix leak of cconf->c.name during config check

During the config check, the post parsing is not performed. Thus, cache filters
are not fully initialized and their cache name are never released. To be able to
release them, a flag is now set when a cache filter is fully initialized. On
deinit, if the flag is not set, it means the cache name must be freed.

The patch should fix #849. No backport needed.

[Cf: Tim is the patch author, but I added the commit message]