fix: return default bucket acl if none exists

We were trying to parse a non existing acl and returning an
internal server error due to invalid json acl data.

If the bucket acl does not exist, return a default acl with the
root account as the owner.

This fixes #1060, but does not address the invalid acl format
from s3cmd reported in #963.

s3api/controllers/base.go

@@ -921,7 +921,7 @@ func (c S3ApiController) ListActions(ctx *fiber.Ctx) error {
 				})
 		}
 
-		res, err := auth.ParseACLOutput(data)
+		res, err := auth.ParseACLOutput(data, parsedAcl.Owner)
 		return SendXMLResponse(ctx, res, err,
 			&MetaOpts{
 				Logger:      c.logger,