[Bug #17780] Fix Method#super_method for module alias

	Method#super_method crashes for aliased module methods because they are
	not defined on a class. This bug was introduced in
	c60aaed1 as part of bug #17130.
	---
	 proc.c                   |  2 +-
	 test/ruby/test_method.rb | 13 +++++++++++++
	 2 files changed, 14 insertions(+), 1 deletion(-)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67945 b2dd03c8-39d4-4d8f-98ff-823fe69b080e