Avoid shadowing ignored errors listAllBuckets() (#5524)
Avoid shadowing ignored errors listAllBuckets() (#5524)

It can happen such that one of the disks that was down would
return 'errDiskNotFound' but the err is preserved due to
loop shadowing which leads to issues when healing the bucket.
aead/minio,krisis/minio,fwessels/minio,abperiasamy/minio,harshavardhana/minio,jimjag/minio,harshavardhana/minio,NitishT/minio,minio/minio,harshavardhana/minio,aead/minio,jimjag/minio,abperiasamy/minio,rushenn/minio,fwessels/minio,balamurugana/minio,vadmeste/minio,krishnasrinivas/minio,vadmeste/minio,rushenn/minio,krisis/minio,donatello/minio,aead/minio,krishnasrinivas/minio,jimjag/minio,abperiasamy/minio,aead/minio,krishnasrinivas/minio,jimjag/minio,fwessels/minio,krishnasrinivas/minio,NitishT/minio,aead/minio,NitishT/minio,aead/minio,abperiasamy/minio,fwessels/minio,harshavardhana/minio,rushenn/minio,aead/minio,harshavardhana/minio,balamurugana/minio,donatello/minio,aead/minio,minio/minio,rushenn/minio,NitishT/minio,harshavardhana/minio,harshavardhana/minio,harshavardhana/minio