return error during part listing when no quorum (#8241)

This commit fixes a subtle bug that (probably)
caused an issue affecting encrypted multipart objects.

When a cluster has no quorum this bug causes `ListObjectParts`
to return nil as error instead of a quorum error.

Thanks to @harshavardhana for detecting this.

cmd/xl-v1-multipart.go

@@ -520,7 +520,7 @@ func (xl xlObjects) ListObjectParts(ctx context.Context, bucket, object, uploadI
 
 	reducedErr := reduceWriteQuorumErrs(ctx, errs, objectOpIgnoredErrs, writeQuorum)
 	if reducedErr == errXLWriteQuorum {
-		return result, toObjectErr(err, minioMetaMultipartBucket, uploadIDPath)
+		return result, toObjectErr(reducedErr, minioMetaMultipartBucket, uploadIDPath)
 	}
 
 	_, modTime := listOnlineDisks(storageDisks, partsMetadata, errs)