[ruby-core:91916] [Ruby trunk Bug#15720] SystemStackError when referencing a refinement in a module that isn't used

Issue #15720 has been reported by chocolateboy (Art Vandelay).

----------------------------------------
Bug #15720: SystemStackError when referencing a refinement in a module that isn't used
https://bugs.ruby-lang.org/issues/15720

* Author: chocolateboy (Art Vandelay)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.7.0dev (2019-03-21 trunk 67332) [x86_64-linux]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
```ruby
module M1
  refine Kernel do
    def foo
      'foo called!'
    end
  end
end

module M2
  refine Kernel do
    def bar
      'bar called!'
    end
  end
end

using M1

puts foo
puts bar
```

Expected:

```
foo called!
Traceback (most recent call last):
bug.rb:22:in `<main>': undefined local variable or method `bar' for main:Object (NameError)
```

Actual:

```
foo called!
Traceback (most recent call last):
bug.rb:22:in `<main>': stack level too deep (SystemStackError)
```

Same result on:

- ruby 2.6.2p47 (2019-03-13 revision 67232) [x86_64-linux]
- ruby 2.7.0dev (2019-03-21 trunk 67332) [x86_64-linux]

---Files--------------------------------
bug.rb (188 Bytes)


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