Incorrect else if condition coverage

[hamishknight]

For e.g:

func foo() {
  if .random() {
    ()
  } else if .random() {
    ()
  } else {
    ()
  }
}

the condition else if .random() is given the region 0, which is incorrect, it should be (0 - 1), i.e it's hit anytime the first if condition isn't true.

rdar://104078910