Revert "Use &. instead of modifier if"

This reverts commit 9d015aa91cc3ec45e41be58fd836fb7f6655a624.

Because tool/extlibs.rb runs with BASERUBY that may be ruby < 2.3

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63617 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/extlibs.rb

@@ -65,7 +65,7 @@ class ExtLibs
     when '.zip'
       pid = Process.spawn("unzip", inp, "-d", dir)
     end
-    f&.close
+    f.close if f
     Process.wait(pid)
     $?.success? or raise "failed to extract #{cache}"
   end