Fix an inner method Range#can_iterate_from?

Prefer protected to private
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* This method is just used by `self.each`.

Replace receiver for X19
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* `first` is gotten the `self.each`

refer
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  * https://github.com/rubinius/rubinius/pull/2272#discussion-diff-3778716
  * #2272
Merge pull request #2273 from kachick/fix-range-can_iterate_from

Fix an inner method Range#can_iterate_from?