kc.c: enforce key/keychain number limit when opening a database
kc.c: enforce key/keychain number limit when opening a database

Until now we didn't check if the opened database has more keychains or
keys per keychains than the allowed maximum (ITEMS_MAX).
Nothing fatal, the user couldn't access the keys/chains above the
maximum anyway.

levaidaniel/kc,levaidaniel/kc,levaidaniel/kc