message: fixed element-index color-scheme
diff: import { ColorScale, Color } from 'mol-util/color';
  import { Location } from 'mol-model/location';
  -import { StructureElement, Link, Unit } from 'mol-model/structure';
  +import { StructureElement, Link } from 'mol-model/structure';
  import { OrderedSet } from 'mol-data/int';
  import { ColorThemeProps, ColorTheme, LocationColor } from '../color';
  @@ -19,22 +19,24 @@ export function ElementIndexColorTheme(props: ColorThemeProps): ColorTheme {
  const { units } = props.structure
  const unitCount = units.length
  const cummulativeElementCount = new Map<number, number>()
  + const unitIdIndex = new Map<number, number>()
  let elementCount = 0
  for (let i = 0; i < unitCount; ++i) {
  cummulativeElementCount.set(i, elementCount)
  elementCount += units[i].elements.length
  + unitIdIndex.set(units[i].id, i)
  }
  - const scale = ColorScale.create({ domain: [ 0, elementCount ] })
  + const scale = ColorScale.create({ domain: [ 0, elementCount - 1 ] })
  color = (location: Location): Color => {
  if (StructureElement.isLocation(location)) {
  - const unitIndex = Unit.findUnitById(location.unit.id, units)
  + const unitIndex = unitIdIndex.get(location.unit.id)!
  const unitElementIndex = OrderedSet.findPredecessorIndex(location.unit.elements, location.element)
  - return scale.color(cummulativeElementCount.get(unitIndex) || 0 + unitElementIndex)
  + return scale.color(cummulativeElementCount.get(unitIndex)! + unitElementIndex)
  } else if (Link.isLocation(location)) {
  - const unitId = Unit.findUnitById(location.aUnit.id, units)
  - return scale.color(cummulativeElementCount.get(unitId) || 0 + location.aIndex)
  + const unitIndex = unitIdIndex.get(location.aUnit.id)!
  + return scale.color(cummulativeElementCount.get(unitIndex)! + location.aIndex)
  }
  return DefaultColor
  }
  