Update S1479: "Switch with too many cases" should ignore empty, fall-through cases

[ganncamp]

Rule S1479

The reasoning behind this rule is

When switch statements have large sets of case clauses, it is usually an attempt to map two sets of data. A real map structure would be more readable and maintainable

But empty, fall-through cases argue against this interpretation. So at the very least they should be ignored by the count. E.G.:

switch (i) {
  case 1:  // ignored
  case 2:  // ignored
  case 3:  // fallthrough but NOT ignored
    DoTheThing();
  case 4:  // counted as usual
    DoTheFinalThing();
    break;
  case 5:
//...