Fix get_random for count != 4k, add randomReader()
Fix get_random for count != 4k, add randomReader()

howeyc/restic,bchapuis/restic,stuertz/restic,rakoo/restic,ar-jan/restic,arithmetric/restic,byo/restic,mappu/restic,middelink/restic,fawick/restic,stuertz/restic,ar-jan/restic,jayme-github/restic,fawick/restic,klauspost/restic,ckemper67/restic,middelink/restic,kurin/restic,intfrr/restic,pombredanne/restic,rakoo/restic,jayme-github/restic,byo/restic,restic/restic,kurin/restic,restic/restic,episource/restic