checker: Validate pack checksums before unpacking
checker: Validate pack checksums before unpacking

This avoids reading a possibly invalid size at the end of a corrupted pack

fawick/restic,fawick/restic,stuertz/restic,bchapuis/restic,jayme-github/restic,stuertz/restic,ar-jan/restic,ckemper67/restic,middelink/restic,kurin/restic,ar-jan/restic,restic/restic,byo/restic,kurin/restic,middelink/restic,byo/restic,jayme-github/restic,arithmetric/restic,restic/restic,mappu/restic