resolv: use safe navigation operator

* lib/resolv.rb (each_address): use safe navigation operator to
  avoid extra hash lookups, as well as each_name since r56890.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61897 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/resolv.rb

@@ -236,9 +236,7 @@ class Resolv
 
     def each_address(name, &proc)
       lazy_initialize
-      if @name2addr.include?(name)
-        @name2addr[name].each(&proc)
-      end
+      @name2addr[name]&.each(&proc)
     end
 
     ##