[ruby-cvs:78749] 9245462499 (master): Replace debug test with assertion

John Hawthorn	2019-12-13 15:43:00 +0900 (Fri, 13 Dec 2019)

  New Revision: 9245462499

  https://github.com/ruby/ruby/commit/9245462499

  Log:
    Replace debug test with assertion
    
    It's a Ruby bug if this ever happens check it as an assertion instead of
    paying the cost of the check every time.

  Modified files:
    vm_method.c