check creation time for database to sanity check if the incremental is valid

[kjetilho]

I came across a server very close to being put into production which got an initial full backup, and then just before entering production, the database was wiped and reinitialised. the LSN was sufficiently similar, so Bareos happily made incremental backups off a bogus base.

(luckily we did not need a restore before discovering the issue :-)