Modify range initialize to prevent segmentation fault.

Initialize `Range->edges` after checking `beg` and `end` to prevent segmentation fault.

If `range_check` raises exception in range.c, segmentation fault occurs
because `Range->edges->beg` and `Range->edges->end` are not initialized.
For example, the following code causes segmentation fault.
```ruby
100000.times do
  begin
    "a" + "b"  # make heap dirty.
    1.."a"
  rescue
  end
end
```