Some #[]?(Range) methods can still raise IndexError

[HertzDevil]

There are 4 types in the standard library that define both #[]?(range : Range) and #[]?(start : Int, count : Int). When the start index is too small, the latter always returns nil, but the first may still raise IndexError nonetheless:

def foo(x)
  a = begin; x[-3, 2]?; rescue ex; ex; end
  b = begin; x[-3..-2]?; rescue ex; ex; end
  c = begin; x[3, 2]?; rescue ex; ex; end
  d = begin; x[3..4]?; rescue ex; ex; end

  {a, b, c, d}
end

foo([0, 0])             # => {nil, nil, nil, nil}
foo(Slice[0, 0])        # => {nil, #<IndexError:Index out of bounds>, nil, nil}
foo("00")               # => {nil, nil, nil, nil}
foo("00".match!(/(.)/)) # => {nil, #<IndexError:Index out of bounds>, nil, nil}

This does not seem to be intended behavior; all kinds of out-of-range calls to #[]? should return nil, not just ones whose range start index is large enough.

(This does not concern with the definition of "out-of-bound" itself, which is currently different for Slice; what matters here is that #[] and #[]? agree on their notions of "out-of-bound".)

(The internal StringScanner::StringMatchData defines only the Range overload. It never raises IndexError.)