function isEmptyIndex (index) {
  for (let i = 0; i < index._dimensions.length; ++i) {
    const dimension = index._dimensions[i]
    if (dimension._data && isArray(dimension._data)) {
      if (dimension._size[0] === 0) {
        return true
      }
    } else if (dimension.isRange) {
      if (dimension.start === dimension.end) {
        return true
      }
    } else if (isString(dimension)) {
      if (dimension.length === 0) {
        return true
      }
    }
  }
  return false
}
Test if an index has empty values
@param {Index} index    Zero-based index