rational.c: canonicalization case
* rational.c (float_numerator, float_denominator): fix for
canonicalization case where `Float#to_r` could return an Integer
not a Rational. although mathn.rb has been removed in the
trunk, fix for the backport purpose.
[ruby-core:80942] [Bug #13528]
merge revision(s) 58523: [Backport #13528]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59510 b2dd03c8-39d4-4d8f-98ff-823fe69b080e